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Subject: Re: [PATCH v2] x86,sched: allow topologies where NUMA nodes share an
 LLC
To: Peter Zijlstra <peterz@infradead.org>,
        Alison Schofield <alison.schofield@intel.com>
References: <20180322204922.GA2337@alison-desk.jf.intel.com>
 <20180322232030.GA4043@hirez.programming.kicks-ass.net>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Luck@alison-desk.jf.intel.com, Tony <tony.luck@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>, Borislav Petkov <bp@alien8.de>,
        David Rientjes <rientjes@google.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Prarit Bhargava <prarit@redhat.com>, brice.goglin@gmail.com,
        x86@kernel.org, linux-kernel@vger.kernel.org
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <84b2c73d-e388-36dd-729e-a5baa4b29d07@linux.intel.com>
Date: Thu, 22 Mar 2018 16:55:48 -0700
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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.