Re: [PATCH v2 02/12] sched/deadline: Less agressive dl_server handling

[Geert Uytterhoeven]

Hi Juri,

On Wed, 30 Jul 2025 at 11:46, Juri Lelli <juri.lelli@xxxxxxxxxx> wrote:
> On 30/07/25 11:34, Geert Uytterhoeven wrote:
> Apologies for interjecting.

No apologies needed, much appreciated!

> > On Wed, 2 Jul 2025 at 14:19, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > Chris reported that commit 5f6bd380c7bd ("sched/rt: Remove default
> > > bandwidth control") caused a significant dip in his favourite
> > > benchmark of the day. Simply disabling dl_server cured things.
> > >
> > > His workload hammers the 0->1, 1->0 transitions, and the
> > > dl_server_{start,stop}() overhead kills it -- fairly obviously a bad
> > > idea in hind sight and all that.
> > >
> > > Change things around to only disable the dl_server when there has not
> > > been a fair task around for a whole period. Since the default period
> > > is 1 second, this ensures the benchmark never trips this, overhead
> > > gone.
> > >
> > > Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server")
> > > Reported-by: Chris Mason <clm@xxxxxxxx>
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > > Link: https://lkml.kernel.org/r/20250520101727.507378961@xxxxxxxxxxxxx
> >
> > Thanks for your patch, which is now commit cccb45d7c4295bbf
> > ("sched/deadline: Less agressive dl_server handling") upstream.
> >
> > This commit causes
> >
> >     sched: DL replenish lagged too much
> >
> > to be printed after full user-space (Debian) start-up on m68k
> > (atari_defconfig running on ARAnyM).  Reverting this commit and fixing
> > the small conflict gets rid of the message.
>
> Does
> https://lore.kernel.org/lkml/20250615131129.954975-1-kuyo.chang@xxxxxxxxxxxx/
> help already (w/o the revert)?

Thanks, it does!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds