-- Thanks Zhou On 09/25/2015 02:50 PM, Dave Young wrote: > Hi, > > On 09/16/15 at 03:50pm, Zhou Wenjian wrote: >> Add descriptions of parallel dumping and how to use it. >> >> Signed-off-by: Zhou Wenjian zhouwj-fnst@cn.fujitsu.com >> --- >> v2->v3: >> 1.address Baoquan He's comment on disable_cpu_apicid >> v1->v2: >> 1.fix some inappropriate description >> 2.delete some unnecessary description >> >> kexec-kdump-howto.txt | 31 +++++++++++++++++++++++++++++++ >> 1 file changed, 31 insertions(+) >> >> diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt >> index 05b497f..6e49f35 100644 >> --- a/kexec-kdump-howto.txt >> +++ b/kexec-kdump-howto.txt >> @@ -616,6 +616,37 @@ options are copied from /proc/cmdline. In general it is best to append >> command line options using "KDUMP_COMMANDLINE_APPEND=" instead of replacing >> the original command line completely. >> >> +Parallel Dumping Operation >> +========================== >> +Kexec allows kdump using multiple cpus. So parallel feature can accelerate >> +dumping substantially, especially in executing compress and filter. > > s/compress/compression > >> +For example: >> + >> + 1."makedumpfile -c --num-threads [THREAD_NUM] /proc/vmcore dumpfile" >> + 2."makedumpfile -c /proc/vmcore dumpfile", >> + >> + 1 has better performance than 2, if THREAD_NUM is larger than two >> + and the usable cpus number is larger than THREAD_NUM. >> + >> +Notes on how to use multiple cpus on a capture kernel on x86 system: >> + >> +Make sure that you are using a kernel that supports disable_cpu_apicid >> +kernel option as a capture kernel, which is needed to avoid x86 specific >> +hardware issue (*). The disable_cpu_apicid kernel option is automatically >> +appended by kdumpctl script and is ignored if the kernel doesn't support it. >> + >> +You need to specify how many cpus to be used in a capture kernel by specifying >> +the number of cpus in nr_cpus kernel option in /etc/sysconfig/kdump. nr_cpus >> +is 1 at default. >> + >> +You should use necessary and suffcient number of cpus on a capture kernel. > > s/suffcient/sufficient > >> +IOW, don't use too many cpus on a capture kernel, or the capture kernel may >> +lead to panic due to Out Of Memory(each cpu uses about 1MB). > > Each cpu uses about 1MB may be not precise, it will depends on kernel, who knows > it use how much in the future. It will use much more on powerpc architecture per > our testing. > > So remove the (each cpu uses about 1MB) and change 'IOW,' to 'Warning: ' sounds > better. > >> + >> +(*) Without disable_cpu_apicid kernel option, capture kernel may lead to >> +hang, system reset or power-off at boot, depending on your system and runtime >> +situation at the time of crash. >> + >> Debugging Tips >> -------------- >> - One can drop into a shell before/after saving vmcore with the help of >> -- >> 1.8.3.1 >> >> _______________________________________________ >> kexec mailing list >> kexec@lists.fedoraproject.org >> https://lists.fedoraproject.org/mailman/listinfo/kexec >> >> > > BTW, if you need a RHEL fix please file a bug again proper version. >