Hi Song, On Thu, 9 May 2019 at 23:54, Song Liu <liu.song....@gmail.com> wrote: > > On Thu, Apr 25, 2019 at 5:38 AM Viresh Kumar <viresh.ku...@linaro.org> wrote: > > > > Hi, > > > > Here is another attempt to get some benefit out of the sched-idle > > policy. The previous version [1] focused on getting better power numbers > > and this version tries to get better performance or lower response time > > for the tasks. > > > > The first patch is unchanged from v1 and accumulates > > information about sched-idle tasks per CPU. > > > > The second patch changes the way the target CPU is selected in the fast > > path. Currently, we target for an idle CPU in select_idle_sibling() to > > run the next task, but in case we don't find idle CPUs it is better to > > pick a CPU which will run the task the soonest, for performance reason. > > A CPU which isn't idle but has only SCHED_IDLE activity queued on it > > should be a good target based on this criteria as any normal fair task > > will most likely preempt the currently running SCHED_IDLE task > > immediately. In fact, choosing a SCHED_IDLE CPU shall give better > > results as it should be able to run the task sooner than an idle CPU > > (which requires to be woken up from an idle state). > > > > Basic testing is done with the help of rt-app currently to make sure the > > task is getting placed correctly. > > I run some test with this set on our (Facebook's) web service (main job) > and ffmpeg (side job). The result looks promising. > > For all the tests below, I run the web service with same load level; and > the side job with SCHED_IDLE. I presented schedule latency distribution > of the main job. The latency distribution is measured with the runqlat tool: > https://github.com/iovisor/bpftrace/blob/master/tools/runqlat.bt > > I modified the tool to only track wake up latency of the main job. > > 4 cases are compared here: > > 1. w/o this set, w/o side job; > 2. w/ this set, w/o side job; > 3. w/o this set, w/ side job; > 4. w/ this set, w/ side job; > > > Case #1. w/o this set, w/o side job > @usecs: > [1] 1705 | > | > [2, 4) 1102086 > |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [4, 8) 329160 |@@@@@@@@@@@@@@@ > | > [8, 16) 34135 |@ > | > [16, 32) 37466 |@ > | > [32, 64) 15700 | > | > [64, 128) 8759 | > | > [128, 256) 5714 | > | > [256, 512) 3718 | > | > [512, 1K) 2152 | > | > [1K, 2K) 882 | > | > [2K, 4K) 256 | > | > [4K, 8K) 48 | > | > [8K, 16K) 2 | > | > > Case #2. w/ this set, w/o side job; > @usecs: > [1] 2121 | > | > [2, 4) 1251877 > |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [4, 8) 401517 |@@@@@@@@@@@@@@@@ > | > [8, 16) 64325 |@@ > | > [16, 32) 74352 |@@@ > | > [32, 64) 40583 |@ > | > [64, 128) 26129 |@ > | > [128, 256) 18612 | > | > [256, 512) 12863 | > | > [512, 1K) 8304 | > | > [1K, 2K) 4072 | > | > [2K, 4K) 1569 | > | > [4K, 8K) 411 | > | > [8K, 16K) 70 | > | > [16K, 32K) 1 | > | > > From #1 and #2, we see this set probably adds a little overhead to > scheduling when there is no side job. But the overhead is clearly very > small. > > > Case #3. w/o this set, w/ side job; > @usecs: > [1] 1282 | > | > [2, 4) 260977 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ > | > [4, 8) 446120 > |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [8, 16) 136927 |@@@@@@@@@@@@@@@ > | > [16, 32) 148758 |@@@@@@@@@@@@@@@@@ > | > [32, 64) 160291 |@@@@@@@@@@@@@@@@@@ > | > [64, 128) 177292 |@@@@@@@@@@@@@@@@@@@@ > | > [128, 256) 184573 |@@@@@@@@@@@@@@@@@@@@@ > | > [256, 512) 173405 |@@@@@@@@@@@@@@@@@@@@ > | > [512, 1K) 149662 |@@@@@@@@@@@@@@@@@ > | > [1K, 2K) 120217 |@@@@@@@@@@@@@@ > | > [2K, 4K) 80275 |@@@@@@@@@ > | > [4K, 8K) 36108 |@@@@ > | > [8K, 16K) 11121 |@ > | > [16K, 32K) 736 | > | > [32K, 64K) 19 | > | > > Case #4. w/ this set, w/ side job; > @usecs: > [1] 407 | > | > [2, 4) 535378 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ > | > [4, 8) 795526 > |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [8, 16) 93032 |@@@@@@ > | > [16, 32) 89890 |@@@@@ > | > [32, 64) 82775 |@@@@@ > | > [64, 128) 84413 |@@@@@ > | > [128, 256) 84413 |@@@@@ > | > [256, 512) 77202 |@@@@@ > | > [512, 1K) 66043 |@@@@ > | > [1K, 2K) 49276 |@@@ > | > [2K, 4K) 30114 |@ > | > [4K, 8K) 11145 | > | > [8K, 16K) 2328 | > | > [16K, 32K) 88 | > | > > #3 and #4 clearly showed the benefit of this set. With this set, we see > significantly fewer latency values in the 8usecs+ ranges. >
Thanks for running tests with this patchset, your results looks goods with a significant decrease of long wakeup latency. Vincent > Thanks, > Song > > > > > -- > > viresh > > > > Viresh Kumar (2): > > sched: Start tracking SCHED_IDLE tasks count in cfs_rq > > sched/fair: Fallback to sched-idle CPU if idle CPU isn't found > > > > kernel/sched/fair.c | 42 +++++++++++++++++++++++++++++++++--------- > > kernel/sched/sched.h | 2 ++ > > 2 files changed, 35 insertions(+), 9 deletions(-) > > > > -- > > 2.21.0.rc0.269.g1a574e7a288b > > > > [1] > > https://lore.kernel.org/lkml/cover.1543229820.git.viresh.ku...@linaro.org/
