From: Mike Galbraith <efault@gmx.de>
To: Tom Gebhardt <tomge68@gmail.com>
Cc: peterz@infradead.org, mingo@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: sched/fair: DELAY_DEQUEUE causes ~25% pipe IPC regression on Raspberry Pi 5
Date: Tue, 21 Apr 2026 15:14:55 +0200 [thread overview]
Message-ID: <3243f2b7d7e5c3121c17fe84c328137f91b322a7.camel@gmx.de> (raw)
In-Reply-To: <CAOX0jgi0xSHfwy63kB9FjGTNS3A6oxaDDHwPUk_L5T2MKEETKQ@mail.gmail.com>
On Tue, 2026-04-21 at 14:46 +0200, Tom Gebhardt wrote:
>
> The fact that your local 6.12.y branch with patches 0047 and 0089
> (Christian's "Prevent negative lag increase during delayed dequeue")
> does not reproduce the issue is very encouraging. It suggests that the
> downstream RPi kernel just hasn't picked up those fixes yet, which
> explains why we still see the regression on stock rpi-6.12.y.
Not sure. Taking stress-ng 0.15.06 to trusty ole x86_64 i4790 desktop
box, since I see no excuse for it to be arch specific, the virgin
6.12.82 DELAY_DEQUEUE delta for a pure voluntary config (lowest
overhead) was -6%. Adding all eevdf backports took it to -3%. To me
that looks very much like a nothing-burger, ie routine bench jitter
when diddling *anything* in fastpaths.
The only clear signal has come from that pi5 6.12.75+rpt-rpi-2712 plus
stress-ng 0.15.06 combo.
-Mike
next prev parent reply other threads:[~2026-04-21 13:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-16 12:22 Tom Gebhardt
2026-04-16 20:04 ` Christian Loehle
2026-04-17 15:42 ` Vincent Guittot
2026-04-18 16:12 ` Tom Gebhardt
2026-04-20 14:27 ` Vincent Guittot
2026-04-20 3:53 ` Mike Galbraith
2026-04-20 10:59 ` Tom Gebhardt
2026-04-21 3:55 ` Mike Galbraith
2026-04-21 12:46 ` Tom Gebhardt
2026-04-21 13:14 ` Mike Galbraith [this message]
2026-04-23 4:51 ` Mike Galbraith
2026-04-23 8:04 ` Peter Zijlstra
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