linux-kernel - Re: IPC drop down on AMD epyc 7702P

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Message-ID: <20250430092516.GJ4439@noisy.programming.kicks-ass.net>
Date: Wed, 30 Apr 2025 11:25:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Jean-Baptiste Roquefere <jb.roquefere@...me.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	"Gautham R. Shenoy" <gautham.shenoy@....com>,
	Swapnil Sapkal <swapnil.sapkal@....com>,
	Valentin Schneider <vschneid@...hat.com>,
	"regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: IPC drop down on AMD epyc 7702P

On Wed, Apr 30, 2025 at 02:43:00PM +0530, K Prateek Nayak wrote:
> (+ more scheduler folks)
> 
> tl;dr
> 
> JB has a workload that hates aggressive migration on the 2nd Generation
> EPYC platform that has a small LLC domain (4C/8T) and very noticeable
> C2C latency.

Seems like the kind of chip the cache aware scheduling crud should be
good for. Of course, it's still early days on that, so it might not be
in good enough shape to help yet.

But long term, that should definitely be the goal, rather than finding
ways to make relax_domain hacks available again.