On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote:
Hi,
I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation.
This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Greg Padgett" gpadgett@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Wednesday, December 19, 2012 3:59:11 PM Subject: Re: [Engine-devel] CPU Overcommit Feature
On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote:
Hi,
I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation.
This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host. We need to be able to tell the difference. So this moves us to cpuCores2 suggestion. This is one possibility (cpuRealCores?), and the alternative is an indication of vdsm config (true/false) which may be removed in the future. I suspect over time cpu and cpu2 will confuse people.
So I'd suggest having the boolean and removing it along with the vdsm configuration in the next ovirt version.
Doron
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote:
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Greg Padgett" gpadgett@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Wednesday, December 19, 2012 3:59:11 PM Subject: Re: [Engine-devel] CPU Overcommit Feature
On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote:
Hi,
I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation.
This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
Dan.
We need to be able to tell the difference. So this moves us to cpuCores2 suggestion. This is one possibility (cpuRealCores?), and the alternative is an indication of vdsm config (true/false) which may be removed in the future. I suspect over time cpu and cpu2 will confuse people.
So I'd suggest having the boolean and removing it along with the vdsm configuration in the next ovirt version.
On 12/20/2012 09:43 AM, Dan Kenigsberg wrote:
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote:
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Greg Padgett" gpadgett@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Wednesday, December 19, 2012 3:59:11 PM Subject: Re: [Engine-devel] CPU Overcommit Feature
On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote:
Hi,
I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation.
This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.
Dan.
We need to be able to tell the difference. So this moves us to cpuCores2 suggestion. This is one possibility (cpuRealCores?), and the alternative is an indication of vdsm config (true/false) which may be removed in the future. I suspect over time cpu and cpu2 will confuse people.
So I'd suggest having the boolean and removing it along with the vdsm configuration in the next ovirt version.
vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote:
On 12/20/2012 09:43 AM, Dan Kenigsberg wrote:
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote:
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Greg Padgett" gpadgett@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Wednesday, December 19, 2012 3:59:11 PM Subject: Re: [Engine-devel] CPU Overcommit Feature
On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote:
Hi,
I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation.
This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.
Note that I do not suggest to drop report_host_threads_as_cores now. I am suggesting to keep on lying even to new Engine. If someone thinks that lying is bad, he should reset report_host_threads_as_cores.
It seems to me that the suggested API is being coerced by a very limited use case, that is not going to be really harmed by a straight-forward API.
Dan.
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Itamar Heim" iheim@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 11:55:10 AM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote:
On 12/20/2012 09:43 AM, Dan Kenigsberg wrote:
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote:
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Greg Padgett" gpadgett@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Wednesday, December 19, 2012 3:59:11 PM Subject: Re: [Engine-devel] CPU Overcommit Feature
On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote:
Hi,
I've been working on a feature to allow CPU Overcommitment of hosts in a cluster. This first stage allows the engine to consider host cpu threads as cores for the purposes of VM resource allocation.
This wiki page has further details, your comments are welcome! http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.
Note that I do not suggest to drop report_host_threads_as_cores now. I am suggesting to keep on lying even to new Engine. If someone thinks that lying is bad, he should reset report_host_threads_as_cores.
It seems to me that the suggested API is being coerced by a very limited use case, that is not going to be really harmed by a straight-forward API.
Dan.
Dan, Did some further checking, and we can go with it; So basically now we add cpuThreads. Additionally, if the report_host_threads_as_cores is turned on, an additional cpuCoresReal will be reported. Since this is a 3.2 cluster feature, the engine will make sure to update the DB with the real numbers, and older clusters will use the information vdsm reports, while blocking the engine side optimization. An update path is already available here: http://gerrit.ovirt.org/#/c/10144/4
I hope that for cluster 3.3 we'll be able to drop the vdsm configuration. A review would be highly appreciated due to the holidays proximity.
Doron
----- Original Message -----
From: "Doron Fediuck" dfediuck@redhat.com To: "Dan Kenigsberg" danken@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 2:14:45 PM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Itamar Heim" iheim@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 11:55:10 AM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote:
On 12/20/2012 09:43 AM, Dan Kenigsberg wrote:
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote:
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Greg Padgett" gpadgett@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Wednesday, December 19, 2012 3:59:11 PM Subject: Re: [Engine-devel] CPU Overcommit Feature
On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett wrote: >Hi, > >I've been working on a feature to allow CPU Overcommitment of >hosts >in a cluster. This first stage allows the engine to consider >host >cpu threads as cores for the purposes of VM resource >allocation. > >This wiki page has further details, your comments are >welcome! >http://www.ovirt.org/Features/cpu_overcommit
I've commented about the vdsm/engine API on http://gerrit.ovirt.org/#/c/10144/ but it is probably better to reiterate it here.
The suggested API is tightly coupled with an ugly hack we pushed to vdsm in order not to solve the issue properly on the first strike.
If we had not have report_host_threads_as_cores, I think we'd have a simpler API reporting only cpuThreads and cpuCores; with no funny boolean flags.
Let us strive to that position as much as we can.
How about asking whoever used report_host_threads_as_cores to unset it once they install Engine 3.2 ? I think that these are very few people, that would not mind this very much.
If this is impossible, I'd add a cpuCores2, always reporting the true number, to be used by new Engines. We may even report it only on the very few cases of report_host_threads_as_cores being set.
Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.
Note that I do not suggest to drop report_host_threads_as_cores now. I am suggesting to keep on lying even to new Engine. If someone thinks that lying is bad, he should reset report_host_threads_as_cores.
It seems to me that the suggested API is being coerced by a very limited use case, that is not going to be really harmed by a straight-forward API.
Dan.
Dan, Did some further checking, and we can go with it; So basically now we add cpuThreads. Additionally, if the report_host_threads_as_cores is turned on, an additional cpuCoresReal will be reported.
No need for that. There is only one problematic state where VDSM cheats and reports cores == threads. This does not happen by mistake, the user specifically asked for it.
The above condition above also happens if threads is really off or the processor does not have threads, so it's a state we need to handle in any case.
So just report threads=off, whenever cores == threads and treat it as such. If the user is unhappy then he should just turn off the cheat mode.
Since this is a 3.2 cluster feature, the engine will make sure to update the DB with the real numbers, and older clusters will use the information vdsm reports, while blocking the engine side optimization. An update path is already available here: http://gerrit.ovirt.org/#/c/10144/4
I hope that for cluster 3.3 we'll be able to drop the vdsm configuration. A review would be highly appreciated due to the holidays proximity.
Doron _______________________________________________ Engine-devel mailing list Engine-devel@ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel
----- Original Message -----
From: "Simon Grinberg" simon@redhat.com To: "Doron Fediuck" dfediuck@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 4:56:14 PM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
----- Original Message -----
From: "Doron Fediuck" dfediuck@redhat.com To: "Dan Kenigsberg" danken@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 2:14:45 PM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Itamar Heim" iheim@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 11:55:10 AM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote:
On 12/20/2012 09:43 AM, Dan Kenigsberg wrote:
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote:
----- Original Message ----- >From: "Dan Kenigsberg" danken@redhat.com >To: "Greg Padgett" gpadgett@redhat.com >Cc: "engine-devel" engine-devel@ovirt.org, >vdsm-devel@fedorahosted.org >Sent: Wednesday, December 19, 2012 3:59:11 PM >Subject: Re: [Engine-devel] CPU Overcommit Feature > >On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett >wrote: >>Hi, >> >>I've been working on a feature to allow CPU Overcommitment >>of >>hosts >>in a cluster. This first stage allows the engine to >>consider >>host >>cpu threads as cores for the purposes of VM resource >>allocation. >> >>This wiki page has further details, your comments are >>welcome! >>http://www.ovirt.org/Features/cpu_overcommit > >I've commented about the vdsm/engine API on >http://gerrit.ovirt.org/#/c/10144/ but it is probably better >to >reiterate it here. > >The suggested API is tightly coupled with an ugly hack we >pushed >to >vdsm >in order not to solve the issue properly on the first >strike. > >If we had not have report_host_threads_as_cores, I think >we'd >have a >simpler API reporting only cpuThreads and cpuCores; with no >funny >boolean flags. > >Let us strive to that position as much as we can. > >How about asking whoever used report_host_threads_as_cores >to >unset >it >once they install Engine 3.2 ? I think that these are very >few >people, >that would not mind this very much. > >If this is impossible, I'd add a cpuCores2, always reporting >the >true >number, to be used by new Engines. We may even report it >only >on >the >very few cases of report_host_threads_as_cores being set. > >Dan.
Hi Dan, Thanks for the review.
I agree simply reporting cores and threads would be the right solution. However, when you have hyperthreading turned off you get cores=threads. This is the same situation you have when hyperthreading turned on, and someone used the vdsm configuration of reporting threads as cores.
So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.
Note that I do not suggest to drop report_host_threads_as_cores now. I am suggesting to keep on lying even to new Engine. If someone thinks that lying is bad, he should reset report_host_threads_as_cores.
It seems to me that the suggested API is being coerced by a very limited use case, that is not going to be really harmed by a straight-forward API.
Dan.
Dan, Did some further checking, and we can go with it; So basically now we add cpuThreads. Additionally, if the report_host_threads_as_cores is turned on, an additional cpuCoresReal will be reported.
No need for that. There is only one problematic state where VDSM cheats and reports cores == threads. This does not happen by mistake, the user specifically asked for it.
The above condition above also happens if threads is really off or the processor does not have threads, so it's a state we need to handle in any case.
So just report threads=off, whenever cores == threads and treat it as such. If the user is unhappy then he should just turn off the cheat mode.
ack.
* <3.2 clusters are not supported. * >=3.2 clusters will assume HT off unless cores < threads.
Some release note is needed for this, so users will be advised to turn off vdsm cheating when upgrading to new 3.2 engine, in case they happen to use it.
Since this is a 3.2 cluster feature, the engine will make sure to update the DB with the real numbers, and older clusters will use the information vdsm reports, while blocking the engine side optimization. An update path is already available here: http://gerrit.ovirt.org/#/c/10144/4
I hope that for cluster 3.3 we'll be able to drop the vdsm configuration. A review would be highly appreciated due to the holidays proximity.
Doron
On Thu, Dec 20, 2012 at 10:17:50AM -0500, Doron Fediuck wrote:
----- Original Message -----
From: "Simon Grinberg" simon@redhat.com To: "Doron Fediuck" dfediuck@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 4:56:14 PM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
----- Original Message -----
From: "Doron Fediuck" dfediuck@redhat.com To: "Dan Kenigsberg" danken@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 2:14:45 PM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
----- Original Message -----
From: "Dan Kenigsberg" danken@redhat.com To: "Itamar Heim" iheim@redhat.com Cc: "engine-devel" engine-devel@ovirt.org, vdsm-devel@fedorahosted.org Sent: Thursday, December 20, 2012 11:55:10 AM Subject: Re: [Engine-devel] [vdsm] CPU Overcommit Feature
On Thu, Dec 20, 2012 at 10:23:55AM +0200, Itamar Heim wrote:
On 12/20/2012 09:43 AM, Dan Kenigsberg wrote:
On Wed, Dec 19, 2012 at 09:53:15AM -0500, Doron Fediuck wrote: > >----- Original Message ----- >>From: "Dan Kenigsberg" danken@redhat.com >>To: "Greg Padgett" gpadgett@redhat.com >>Cc: "engine-devel" engine-devel@ovirt.org, >>vdsm-devel@fedorahosted.org >>Sent: Wednesday, December 19, 2012 3:59:11 PM >>Subject: Re: [Engine-devel] CPU Overcommit Feature >> >>On Mon, Dec 17, 2012 at 09:37:57AM -0500, Greg Padgett >>wrote: >>>Hi, >>> >>>I've been working on a feature to allow CPU Overcommitment >>>of >>>hosts >>>in a cluster. This first stage allows the engine to >>>consider >>>host >>>cpu threads as cores for the purposes of VM resource >>>allocation. >>> >>>This wiki page has further details, your comments are >>>welcome! >>>http://www.ovirt.org/Features/cpu_overcommit >> >>I've commented about the vdsm/engine API on >>http://gerrit.ovirt.org/#/c/10144/ but it is probably better >>to >>reiterate it here. >> >>The suggested API is tightly coupled with an ugly hack we >>pushed >>to >>vdsm >>in order not to solve the issue properly on the first >>strike. >> >>If we had not have report_host_threads_as_cores, I think >>we'd >>have a >>simpler API reporting only cpuThreads and cpuCores; with no >>funny >>boolean flags. >> >>Let us strive to that position as much as we can. >> >>How about asking whoever used report_host_threads_as_cores >>to >>unset >>it >>once they install Engine 3.2 ? I think that these are very >>few >>people, >>that would not mind this very much. >> >>If this is impossible, I'd add a cpuCores2, always reporting >>the >>true >>number, to be used by new Engines. We may even report it >>only >>on >>the >>very few cases of report_host_threads_as_cores being set. >> >>Dan. > >Hi Dan, >Thanks for the review. > >I agree simply reporting cores and threads would be the right >solution. >However, when you have hyperthreading turned off you get >cores=threads. >This is the same situation you have when hyperthreading >turned >on, and >someone used the vdsm configuration of reporting threads as >cores. > >So the engine won't know the real status of the host.
This is not surprising, as report_host_threads_as_cores means in blunt English "lie to Engine about the number of cores". The newly suggested flag says "don't believe what I said in cpuCores, since I'm lying". Next thing we'd have is another flag saying that the former flag was a lie, and cpuCores is actually trustworthy.
Instead of dancing this dance, I suggest to stop lying.
report_host_threads_as_cores was a hack to assist a older Engine versions. Engine users that needed it had to set it out-of-band on their hosts. Now if they upgrade their Engine, they can -- as easily -- reset that value.
If they forget, nothing devastating happens beyond Engine assuming that hyperthreading is off.
Please consider this suggestion. I find it the simplest for all involved parties.
the only problem is the new vdsm doesn't know which engine may be using it. if engine would say "getVdsCaps engineVersion=3.2", then vdsm could know engine no longer needs lying to and ignore the flag, re-using same field.
Note that I do not suggest to drop report_host_threads_as_cores now. I am suggesting to keep on lying even to new Engine. If someone thinks that lying is bad, he should reset report_host_threads_as_cores.
It seems to me that the suggested API is being coerced by a very limited use case, that is not going to be really harmed by a straight-forward API.
Dan.
Dan, Did some further checking, and we can go with it; So basically now we add cpuThreads. Additionally, if the report_host_threads_as_cores is turned on, an additional cpuCoresReal will be reported.
No need for that. There is only one problematic state where VDSM cheats and reports cores == threads. This does not happen by mistake, the user specifically asked for it.
The above condition above also happens if threads is really off or the processor does not have threads, so it's a state we need to handle in any case.
So just report threads=off, whenever cores == threads and treat it as such. If the user is unhappy then he should just turn off the cheat mode.
ack.
- <3.2 clusters are not supported.
Some release note is needed for this, so users will be advised to turn off vdsm cheating when upgrading to new 3.2 engine, in case they happen to use it.
Plain and simple. vdsm side accepted to master branch. Please backport it to the ovirt-3.2 branch in order to get into the release.
vdsm-devel@lists.stg.fedorahosted.org
-
Dan Kenigsberg -
dfediuck＠redhat.com -
iheim＠redhat.com -
Simon Grinberg