linux-kernel - Re: [PATCH v2 00/12] sched: Address schbench regression

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Message-ID: <20250708190201.GE477119@noisy.programming.kicks-ass.net>
Date: Tue, 8 Jul 2025 21:02:01 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, clm@...a.com
Subject: Re: [PATCH v2 00/12] sched: Address schbench regression

On Mon, Jul 07, 2025 at 11:49:17PM +0530, Shrikanth Hegde wrote:

> Git bisect points to
> # first bad commit: [dc968ba0544889883d0912360dd72d90f674c140] sched: Add ttwu_queue support for delayed tasks

Moo.. Are IPIs particularly expensive on your platform?

The 5 cores makes me think this is a partition of sorts, but IIRC the
power LPAR stuff was fixed physical, so routing interrupts shouldn't be
much more expensive vs native hardware.

> Note:
> at commit: "sched: Change ttwu_runnable() vs sched_delayed" there is a small regression.

Yes, that was more or less expected. I also see a dip because of that
patch, but its small compared to the gains gotten by the previous
patches -- so I was hoping I'd get away with it :-)