Messages in this thread |  | | | Date | Wed, 27 Apr 2011 11:54:54 -0500 | | From | Dave Kleikamp <> | | Subject | Re: [PATCH 00/21] sched: Reduce runqueue lock contention -v6 |
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On 04/05/2011 10:23 AM, Peter Zijlstra wrote: > This patch series aims to optimize remote wakeups by moving most of the > work of the wakeup to the remote cpu and avoid bouncing runqueue data > structures where possible. > > As measured by sembench (which basically creates a wakeup storm) on my > dual-socket westmere: > > $ for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance> $i; done > $ echo 4096 32000 64 128> /proc/sys/kernel/sem > $ ./sembench -t 2048 -w 1900 -o 0 > > unpatched: run time 30 seconds 647278 worker burns per second > patched: run time 30 seconds 816715 worker burns per second > > I've queued this series for .40.
Here are the results of running sembench on a 128 cpu box. In all of the below cases, I had to use the kernel parameter idle=mwait to eliminate spinlock contention in clockevents_notify() in the idle loop. I'll try to track down what can be done about that later.
I took Peter's patches from the tip/sched/locking tree. I got similar results directly from that branch, but separated them out to try to isolate some irregular behavior that mostly went away when I added idle=mwait. Since that branch was on top of 2.6.39-rc3, I used that as a base.
The other patchset in play is Chris Mason's semtimedop optimization patches. By themselves, I didn't see an improvement with Chris' patches, but in conjunction with Peter's, they gave the best results. When combining the patches, I removed Chris' batched wakeup patch, since it conflicted with Peter's patchset and really isn't needed any more.
(It's been a while since Chris posted these. They are in the "unbreakable" git tree, http://oss.oracle.com/git/?p=linux-2.6-unbreakable.git;a=summary , and ported easily to mainline. I can repost them.)
I used Chris's latest sembench, http://oss.oracle.com/~mason/sembench.c and the command "./sembench -t 2048 -w 1900 -o 0". I got similar burns-per-second numbers when cranking up the parameters to "./sembench -t 16384 -w 15000 -o 0".
2.6.38:
2048 threads, waking 1900 at a time using ipc sem operations main thread burns: 6549 worker burn count total 12443100 min 6068 max 6105 avg 6075 run time 30 seconds 414770 worker burns per second
2.6.39-rc3:
worker burn count total 11876900 min 5791 max 5805 avg 5799 run time 30 seconds 395896 worker burns per second
2.6.39-rc3 + mason's semtimedop patches:
worker burn count total 9988300 min 4868 max 4896 avg 4877 run time 30 seconds 332943 worker burns per second
2.6.39-rc3 + mason's patches (no batch wakeup patch):
worker burn count total 9743200 min 4750 max 4786 avg 4757 run time 30 seconds 324773 worker burns per second
2.6.39-rc3 + peterz's patches:
worker burn count total 14430500 min 7038 max 7060 avg 7046 run time 30 seconds 481016 worker burns per second
2.6.39-rc3 + mason's patches + peterz's patches:
worker burn count total 15072700 min 7348 max 7381 avg 7359 run time 30 seconds 502423 worker burns per second
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