Messages in this thread |  | | From | Vincent Guittot <> | Date | Mon, 10 Oct 2016 20:29:01 +0200 | Subject | Re: [PATCH] sched/fair: Do not decay new task load on first enqueue |
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On 10 October 2016 at 15:54, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > On 10/10/16 13:29, Vincent Guittot wrote: >> On 10 October 2016 at 12:01, Matt Fleming <matt@codeblueprint.co.uk> wrote: >>> On Sun, 09 Oct, at 11:39:27AM, Wanpeng Li wrote: >>>> >>>> The difference between this patch and Peterz's is your patch have a >>>> delta since activate_task()->enqueue_task() does do update_rq_clock(), >>>> so why don't have the delta will cause low cpu machines (4 or 8) to >>>> regress against your another reply in this thread? >>> >>> Both my patch and Peter's patch cause issues with low cpu machines. In >>> <20161004201105.GP16071@codeblueprint.co.uk> I said, >>> >>> "This patch causes some low cpu machines (4 or 8) to regress. It turns >>> out they regress with my patch too." >>> >>> Have I misunderstood your question? >>> >>> I ran out of time to investigate this last week, though I did try all >>> proposed patches, including Vincent's, and none of them produced wins >>> across the board. >> >> I have tried to reprocude your issue on my target an hikey board (ARM >> based octo cores) but i failed to see a regression with commit >> 7dc603c9028e. Neverthless, i can see tasks not been well spread > > Wasn't this about the two patches mentioned in this thread? The one from > Matt using 'se->sum_exec_runtime' in the if condition in > enqueue_entity_load_avg() and Peterz's conditional call to > update_rq_clock(rq) in enqueue_task()?
I was trying to reproduce the regression that Matt mentioned at the beg of the thread not those linked to proposed fixes
> >> during fork as you mentioned. So I have studied a bit more the >> spreading issue during fork last week and i have a new version of my >> proposed patch that i'm going to send soon. With this patch, i can see >> a good spread of tasks during the fork sequence and some kind of perf >> improvement even if it's bit difficult as the variance is quite >> important with hackbench test so it's mainly an improvement of >> repeatability of the result > > Hikey (ARM64 2x4 cpus) board: cpufreq: performance, cpuidle: disabled > > Performance counter stats for 'perf bench sched messaging -g 20 -l 500' > (10 runs): > > (1) tip/sched/core: commit 447976ef4fd0 > > 5.902209533 seconds time elapsed ( +- 0.31% )
This seems to be too long to test the impact of the forking phase of hackbench
> > (2) tip/sched/core + original patch on the 'sched/fair: Do not decay > new task load on first enqueue' thread (23/09/16) > > 5.919933030 seconds time elapsed ( +- 0.44% ) > > (3) tip/sched/core + Peter's ENQUEUE_NEW patch on the 'sched/fair: Do > not decay new task load on first enqueue' thread (28/09/16) > > 5.970195534 seconds time elapsed ( +- 0.37% ) > > Not sure if we can call this a regression but it also shows no > performance gain. > >>> >>> I should get a bit further this week. >>> >>> Vincent, Dietmar, did you guys ever get around to submitting your PELT >>> tracepoint patches? Getting some introspection into the scheduler's >> >> My tarcepoint are not in a shape to be submitted and would need a >> cleanup as some are more hacks for debugging than real trace events. >> Nevertheless, i can push them on a git branch if they can be useful >> for someone > > We carry two trace events locally, one for PELT on se and one for > cfs_rq's (I have to add the runnable bits here) which work for > CONFIG_FAIR_GROUP_SCHED and !CONFIG_FAIR_GROUP_SCHED. I put them into > __update_load_avg(), attach_entity_load_avg() and > detach_entity_load_avg(). I could post them but so far mainline has been > reluctant to see the need for PELT related trace events ... > > [...]
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