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

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Message-ID: <20150720151831.GK13082@suse.de>
Date:	Mon, 20 Jul 2015 17:18:31 +0200
From:	Joerg Roedel <jroedel@...e.de>
To:	Borislav Petkov <bp@...en8.de>
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 05:10:00PM +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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