linux-kernel - Re: [PATCH] x86/smpboot: Check for cpu

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Date:	Mon, 20 Jul 2015 17:27:44 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Joerg Roedel <jroedel@...e.de>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Joerg Roedel <joro@...tes.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/smpboot: Check for cpu_active on cpu initialization

On Mon, Jul 20, 2015 at 05:18:31PM +0200, Joerg Roedel wrote:
> On Mon, Jul 20, 2015 at 05:10:00PM +0200, Borislav Petkov wrote:
> > On Mon, Jul 20, 2015 at 05:02:40PM +0200, Joerg Roedel wrote:
> > > I have seen a report where this happens on bare metal, when the change
> > > to the cpu_active bit becomes visible on the other CPU significantly
> > > later than the the cpu_online bit. This happened on a pretty big machine
> > > with 88 cores.
> > 
> > So how about what I proposed at the end of my previous mail?
> 
> Oh sorry, I missed that. Setting cpu_active first should work on x86,
> where writes become visible in the order they are executed. But this
> function is in generic code and I have no idea what this change might
> break on other architectures.
> 
> In the end cpu_active means that the scheduler can push tasks to the
> CPU, no idea if some arch code breaks when the scheduler is already
> working on a CPU before it becomes visibly online.

Hmm...

Let's run it by Peter.

@Peter: see the first patch in the mail for the problem of which cpumask
bit to test wrt scheduler and migrating tasks to newly appearing
cores...

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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