linux-kernel - Re: [PATCH v2] x86,sched: allow topologies where NUMA nodes share an LLC

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Date:   Thu, 22 Mar 2018 16:55:48 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Alison Schofield <alison.schofield@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Luck@...son-desk.jf.intel.com,
        Tony <tony.luck@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        David Rientjes <rientjes@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>, brice.goglin@...il.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86,sched: allow topologies where NUMA nodes share an
 LLC

On 03/22/2018 04:20 PM, Peter Zijlstra wrote:
>> +		/*
>> +		 * Return value doesn't actually matter because we
>> +		 * are throwing away coregroups for scheduling anyway.
>> +		 * Return false to bypass topology broken bug messages
>> +		 * and fixups in sched_domain().
>> +		 */
>> +		return false;
> IIRC that return value _does_ matter because the resulting mask still
> ends up user visible in sysfs.
> 
> IIRC I went over with this dhansen a week or so ago, but I cannot now
> recall what we settled on as being the right return value and for what
> reason.

IIRC, a 'return true' true keeps the topology information and a 'return
false' throws it away.  We chose 'false' here because without it some
other warnings showed up in another part of the code:

BUG: arch topology borken the MC domain not a subset of the NODE domain

I think the right thing to do is just remove the first sentence of the
comment.