linux-kernel - Re: [PATCH 2/2] perf/x86/intel/uncore: With > 8 nodes, get pci bus die id from NUMA info

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Date:   Tue, 12 Jan 2021 13:42:46 -0600
From:   Steve Wahl <steve.wahl@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steve Wahl <steve.wahl@....com>, rja_direct@...ups.int.hpe.com,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        "Liang, Kan" <kan.liang@...el.com>
Subject: Re: [PATCH 2/2] perf/x86/intel/uncore: With > 8 nodes, get pci bus
 die id from NUMA info

On Tue, Jan 12, 2021 at 04:07:15PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 11, 2021 at 09:45:16AM -0600, Steve Wahl wrote:
> > On Mon, Jan 11, 2021 at 02:00:33PM +0100, Peter Zijlstra wrote:
> > > On Fri, Jan 08, 2021 at 09:35:49AM -0600, Steve Wahl wrote:
> > > 
> > > 
> > > > +		/*
> > > > +		 * The nodeid and idmap registers only contain enough
> > > > +		 * information to handle 8 nodes.  On systems with more
> > > > +		 * than 8 nodes, we need to rely on NUMA information,
> > > > +		 * filled in from BIOS supplied information, to determine
> > > > +		 * the topology.
> > > > +		 */
> > > 
> > > Egads.. do we realy have to trust BIOS data? BIOS crud tends to be
> > > bonghits qualitee :/
> > 
> > I work too close to BIOS people (virtually, at least for the moment)
> > to safely make disparaging remarks. :-) While the origin is the BIOS,
> > I'm using pieces that were already being pulled from the BIOS tables
> > for NUMA purposes.
> 
> :-) It's just that we've had too much 'fun' with PCI node bindings in
> the past.

I wasn't aware of that, but I understand.  Fortunately, this patch
should't touch cases that aren't already broken (>8 nodes); working
cases continue to use the existing methods.

Thanks!

--> Steve Wahl

-- 
Steve Wahl, Hewlett Packard Enterprise