Re: [RFC][PATCH 0/5] sched: Try and address some recent-ish regressions

[Peter Zijlstra <peterz@infradead.org>]

On Thu, May 29, 2025 at 12:18:54PM +0200, Beata Michalska wrote:
> On Wed, May 28, 2025 at 09:59:44PM +0200, Peter Zijlstra wrote:
> > On Tue, May 20, 2025 at 11:45:38AM +0200, Peter Zijlstra wrote:
> > 
> > > Anyway, the patches are stable (finally!, I hope, knock on wood) but in a
> > > somewhat rough state. At the very least the last patch is missing ttwu_stat(),
> > > still need to figure out how to account it ;-)
> > > 
> > > Chris, I'm hoping your machine will agree with these numbers; it hasn't been
> > > straight sailing in that regard.
> > 
> > Anybody? -- If no comments I'll just stick them in sched/core or so.
> >
> Hi Peter,
> 
> I've tried out your series on top of 6.15 on an Ampere Altra Mt Jade
> dual-socket (160-core) system, which enables SCHED_CLUSTER (2-core MC domains).

Ah, that's a radically different system than what we set out with. Good
to get some feedback on that indeed.

> Sharing preliminary test results of 50 runs per setup as, so far, the data
> show quite a bit of run-to-run variability - not sure how useful those will be.

Yeah, I had some of that on the Skylake system, I had to disable turbo
for the numbers to become stable enough to say anything much.

> At this point without any deep dive, which is probably needed and hopefully
> will come later on.
> 
> 
> Results for average rps (60s) sorted based on P90
> 
> CFG |   min      |  max       |   stdev    |   90th
> ----+------------+------------+------------+-----------
>  1  | 704577.50  | 942665.67  | 46439.49   | 891272.09
>  2  | 647163.57  | 815392.65  | 35559.98   | 783884.00
>  3  | 658665.75  | 859520.32  | 50257.35   | 832174.80

>  4  | 656313.48  | 877223.85  | 47871.43   | 837693.28
>  5  | 630419.62  | 842170.47  | 47267.52   | 815911.81
> 
> Legend:
> #1 : kernel 6.9
> #2 : kernel 6.15
> #3 : kernel 6.15 patched def (TTWU_QUEUE_ON_CPU + NO_TTWU_QUEUE_DEFAULT)
> #4 : kernel 6.15 patched + TTWU_QUEUE_ON_CPU + TTWU_QUEUE_DEFAULT
> #5 : kernel 6.15 patched + NO_TTWU_QUEUE_ON_CPU + NO_TTWU_QUEUE_DEFAULT

Right, minor improvement. At least its not making it worse :-)

The new toy is TTWU_QUEUE_DELAYED, and yeah, I did notice that disabling
TTWU_QUEUE_ON_CPU was a bad idea.