[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20231007220400.GA5581@noisy.programming.kicks-ass.net>
Date: Sun, 8 Oct 2023 00:04:00 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Youssef Esmat <youssefesmat@...omium.org>
Cc: Daniel Jordan <daniel.m.jordan@...cle.com>, mingo@...nel.org,
vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
juri.lelli@...hat.com, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com, corbet@....net, qyousef@...alina.io,
chris.hyser@...cle.com, patrick.bellasi@...bug.net, pjt@...gle.com,
pavel@....cz, qperret@...gle.com, tim.c.chen@...ux.intel.com,
joshdon@...gle.com, timj@....org, kprateek.nayak@....com,
yu.c.chen@...el.com, joel@...lfernandes.org, efault@....de,
tglx@...utronix.de
Subject: Re: [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr
On Thu, Oct 05, 2023 at 02:05:57PM +0200, Peter Zijlstra wrote:
> t=10 V=4 t=10 V=4
> A |----< A |----<
> B |< >B |<
> >C |----------------< C |----------------<
> |---*-----|---------|---------|---------|---- |---*-----|---------|---------|---------|----
>
>
> t=52 V=18 t=36 V=13
> A |----< A |----<
> >B |< B |<
> C |----------------< >C |----------------<
> |---------|-------*-|---------|---------|---- |---------|--*------|---------|---------|----
>
>
> BAaaBCccccccccBBBAaaBBBAaaBB BBAaaBBBAaaBBBAaaBCccccccccB
>
>
>
> As I wrote before; EVDF has worse lag bounds, but this is not
> insurmountable. The biggest problem that I can see is that of wakeup
> preemption. Currently we allow to preempt when 'current' has reached V
> (RUN_TO_PARITY in pick_eevdf()).
>
> With these rules, when EEVDF schedules C (our large slice task) at t=10
> above, it is only a little behind C and can be reaily preempted after
> about 2 time units.
>
> However, EVDF will delay scheduling C until much later, see how A and B
> walk far ahead of V until t=36. Only when will we pick C. But this means
> that we're firmly stuck with C for at least 11 time units. A newly
> placed task will be around V and will have no chance to preempt.
Playing around with it a little:
EEVDF EVDF
slice 30000000 slice 30000000
# Min Latencies: 00014 # Min Latencies: 00048
# Avg Latencies: 00692 # Avg Latencies: 188239
# Max Latencies: 94633 # Max Latencies: 961241
slice 3000000 slice 3000000
# Min Latencies: 00054 # Min Latencies: 00055
# Avg Latencies: 00522 # Avg Latencies: 00673
# Max Latencies: 41475 # Max Latencies: 13297
slice 300000 slice 300000
# Min Latencies: 00018 # Min Latencies: 00024
# Avg Latencies: 00344 # Avg Latencies: 00056
# Max Latencies: 20061 # Max Latencies: 00860
So while it improves the short slices, it completely blows up the large
slices -- utterly slaughters the large slices in fact.
And all the many variants of BIAS_ELIGIBLE that I've tried so far only
manage to murder the high end while simultaneously not actually helping
the low end -- so that's a complete write off.
By far the sanest option so far is PLACE_SLEEPER -- and that is very
much not a nice option either :-(
Powered by blists - more mailing lists