Messages in this thread | | | Date | Wed, 4 Oct 2023 18:24:39 +0200 (CEST) | From | Julia Lawall <> | Subject | Re: EEVDF and NUMA balancing |
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On Wed, 4 Oct 2023, Peter Zijlstra wrote:
> On Wed, Oct 04, 2023 at 02:01:26PM +0200, Julia Lawall wrote: > > > > > > On Tue, 3 Oct 2023, Peter Zijlstra wrote: > > > > > On Tue, Oct 03, 2023 at 10:25:08PM +0200, Julia Lawall wrote: > > > > Is it expected that the commit e8f331bcc270 should have an impact on the > > > > frequency of NUMA balancing? > > > > > > Definitely not expected. The only effect of that commit was supposed to > > > be the runqueue order of tasks. I'll go stare at it in the morning -- > > > definitely too late for critical thinking atm. > > > > Maybe it's just randomly making a bad situation worse rather than directly > > introduing a problem. There is a high standard deviatind in the > > performance. Here are some results with hyperfine. The general trends > > are reproducible. > > OK,. I'm still busy trying to bring a 4 socket machine up-to-date... > gawd I hate the boot times on those machines :/ > > But yeah, I was thinking similar things, I really can't spot an obvious > fail in that commit. > > I'll go have a poke once the darn machine is willing to submit :-)
I tried a two-socket machine, but in 50 runs the problem doesn't show up.
The commit e8f331bcc270 starts with
- if (sched_feat(PLACE_LAG) && cfs_rq->nr_running > 1) { + if (sched_feat(PLACE_LAG) && cfs_rq->nr_running) {
This seemed like a big change - cfs_rq->nr_running > 1 should be rarely true in ua, while cfs_rq->nr_running should always be true. Adding back the > 1 and simply replacing the test by 0 both had no effect, though.
julia
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