linux-kernel - Re: [tip: sched/core] sched: Add cluster scheduler level for x86

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Date:   Fri, 22 Oct 2021 15:36:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>, x86@...nel.org
Subject: Re: [tip: sched/core] sched: Add cluster scheduler level for x86

On Fri, Oct 22, 2021 at 08:31:40AM -0500, Tom Lendacky wrote:
> On 10/20/21 3:40 PM, Peter Zijlstra wrote:
> >   arch/x86/kernel/smpboot.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> > index 849159797101..c2671b2333d1 100644
> > --- a/arch/x86/kernel/smpboot.c
> > +++ b/arch/x86/kernel/smpboot.c
> > @@ -472,7 +472,7 @@ static bool match_l2c(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
> >   	/* Do not match if we do not have a valid APICID for cpu: */
> >   	if (per_cpu(cpu_l2c_id, cpu1) == BAD_APICID)
> > -		return false;
> > +		return match_smt(c, o); /* assume at least SMT shares L2 */
> 
> This does eliminate the message and seems like an appropriate thing to do,
> in general, if the l2c id is not set.
> 
> We're looking into setting the l2c id for AMD platforms, but need to test
> against some older platforms. We'll let you know the results next week.
> 
> In the mean time, it is probably best to at least apply your above patch.

OK, I'll go write up a Changelog and stick on your Reported- and
Tested-by tags.

Thanks!