Date: Mon, 20 Jul 2015 17:18:31 +0200
From: Joerg Roedel <jroedel@suse.de>
To: Borislav Petkov <bp@alien8.de>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/smpboot: Check for cpu_active on cpu initialization
Message-ID: <20150720151831.GK13082@suse.de>
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 <20150720150240.GJ13082@suse.de>
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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.


	Joerg

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