linux-kernel - Re: [PATCH v3] sched/topology: Enable topology_span

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Message-ID: <0835864f-6dc5-430d-91c0-b5605007d9d2@amd.com>
Date: Wed, 5 Feb 2025 15:43:54 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Peter Zijlstra <peterz@...radead.org>
CC: Naman Jain <namjain@...ux.microsoft.com>, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Steve Wahl
	<steve.wahl@....com>, Saurabh Singh Sengar <ssengar@...ux.microsoft.com>,
	<srivatsa@...il.mit.edu>, Michael Kelley <mhklinux@...look.com>
Subject: Re: [PATCH v3] sched/topology: Enable topology_span_sane check only
 for debug builds

Hello Peter,

Thank you for the background!

On 2/5/2025 3:25 PM, Peter Zijlstra wrote:
> On Wed, Feb 05, 2025 at 03:18:24PM +0530, K Prateek Nayak wrote:
> 
>> Have there been any reports on an x86 system / VM where
>> topology_span_sane() was tripped?
> 
> At the very least Intel SNC 'feature' tripped it at some point. They
> figured it made sense to have the LLC span two nodes.
> 
> But I think there were some really dodgy VMs too.
> 
> But yeah, its not been often. But basically dodgy BIOS/VM data can mess
> up things badly enough for it to trip.

Has it ever happened without tripping the topology_sane() check first
on the x86 side?

-- 
Thanks and Regards,
Prateek