Messages in this thread | | | Date | Mon, 11 Mar 2013 09:21:05 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] sched: wakeup buddy |
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* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Wed, 2013-03-06 at 15:06 +0800, Michael Wang wrote: > > > wake_affine() stuff is trying to bind related tasks closely, but it > > doesn't work well according to the test on 'perf bench sched pipe' > > (thanks to Peter). > > so sched-pipe is a poor benchmark for this.. > > Ideally we'd write a new benchmark that has some actual data footprint > and we'd measure the cost of tasks being apart on the various cache > metrics and see what affine wakeup does for it.
Ideally we'd offer applications a new, lightweight vsyscall:
void sys_sched_work_tick(void)
Or, to speed up adoption, a new, vsyscall-accelerated prctrl():
prctl(PR_WORK_TICK);
which applications could call in each basic work unit they are performing.
Sysbench would call it for every transaction completed, sched-pipe would call it for every pipe message sent, hackbench would call it for messages, etc. etc.
This is a minimal application level change, but gives *huge* information to the scheduler: we could balance tasks to maximize their observed work rate.
The scheduler could also do other things, like observe the wakeup/sleep patterns within a 'work atom', observe execution overlap between work atoms and place tasks accordingly, etc. etc.
Today we approximate work atoms by saying that scheduling atoms == work atoms. But that approximation breaks down in a number of important cases.
If we had such a design we'd be able to fix pretty much everything, without the catch-22 problems we are facing normally.
An added bonus would be increased instrumentation: we could trace, time, profile work atom rates and could collect work atom profiles. We see work atom execution histograms, etc. etc. - stuff that is simply not possible today without extensive application-dependent instrumentation.
We could also use utrace scripts to define work atoms without modifying the application: for many applications we know which particular function call means that a basic work unit was completed.
I have actually written the prctl() approach before, for instrumentation purposes, and it does wonders to system analysis.
Any objections?
Thanks,
Ingo
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