Il giorno 12 dic 2018, alle ore 20:30, Chris Murphy lists@colorremedies.com ha scritto:
Really Readding devel@ this time...
On Wed, Dec 12, 2018 at 11:08 AM stan stanl-fedorauser@vfemail.net wrote:
On Tue, 11 Dec 2018 11:48:29 -0000 "Alan Jenkins" alan.christopher.jenkins@gmail.com wrote:
[3] BFQ: http://algo.ing.unimo.it/people/paolo/disk_sched/description.php
[4] https://unix.stackexchange.com/questions/375600/how-to-enable-and-use-the-bf...
[5] "I'd prefer if the distros would lead the way on this, as theyare the ones that will most likely see the most bug reports" - Jens Axboe, https://www.spinics.net/lists/linux-block/msg31062.html
I compiled a custom kernel from the fedora src.rpm for 4.19.8. I turned off all schedulers except NOOP and BFQ. But there was no way in the configuration process (make menuconfig) to set BFQ as default. I tried setting it in kernel-local, but the build process errored because it said NOOP is the default and that disagreed with my choice. I'm running the kernel and it is using noop. And there is no way to change it in the /sys hierarchy.
So, how do I get a fedora kernel to run BFQ?
Short version: Yep, so far in 4.20 there is neither a CONFIG_DEFAULT_BFQ or CONFIG_DEFAULT_IOSCHED="bfq" near as I can tell. Maybe it's different for 4.21.
Yep, hundreds of kilobytes of email have been spent trying to convince Jens Axboe that a default option had to be kept for blk-mq too. At no avail. If anyone wants to restart this fight, I'll be on your side.
I used two boot params: scsi_mod.use_blk_mq=1
Yes, this is needed to switch to blk-mq, until 4.21, when there will be no legacy block any longer. One can also set the corresponding option in the kernel configuration.
elevator=bfq.
I'm not sure this option works with blkmq. IIRC doing this may even cause system failures with blk-mq (but maybe this has been fixed). AFAIK, the only way is to set bfq manually or through, e.g., dev rules, but YMMV.
I don't think that's a good way for a distribution to set the default though.
Icky version:
I set the following in /etc/default/grub and then ran grub2-mkconfig (not on Rawhide!) GRUB_CMDLINE_LINUX="scsi_mod.use_blk_mq=1 elevator=bfq zswap.enabled=1 zswap.max_pool_percent=25 zswap.compressor=lz4"
I also created /etc/dracut.conf.d/bfq.conf containing: add_drivers+=" bfq " yes, with spaces, and rebuilt the initramfs
But upon reboot, total implosion. Piles of USB errors and disconnects (the boot device is a Samsung FIT USB stick which fits flush in an Intel NUC). I didn't have time to troubleshoot what's causing this problem, other than to plug the USB stick into another computer to verify the stick is good and hasn't been corrupted. It's possibly related the mq-blk bug in 4.19.0 through 4.19.7 - so I've since upgraded to 4.19.8 which as those patches, but I haven't had a chance to retest.
I doubt this is bfq fault, as bfq is rather frequently used for USB too. Probably bfq has not been activated at all.
Paolo
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