linux-kernel - Re: [PATCH] x86: Use clflush() instead of wbinvd() whenever possible when changing mapping

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Message-ID: <20090724131649.GC2045@basil.fritz.box>
Date:	Fri, 24 Jul 2009 15:16:49 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Hellstrom <thellstrom@...are.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"venkatesh.pallipadi@...el.com" <venkatesh.pallipadi@...el.com>
Subject: Re: [PATCH] x86: Use clflush() instead of wbinvd() whenever
	possible when changing mapping

> No. It was motivated by the assumption that wbinvd() is just bad:

Ok, got it now.

> Qoute:
>
> WBINVD is a very nasty operation. I was talking to some CPU people and they 
> really recommended to get rid of it as far as possible. Stopping the CPU 
> for msecs is just wrong and there are apparently even some theoretical live 
> lock situations. - It is not interruptible in earlier VT versions and 
> messes up real time in the hypervisor. Some people were doing KVM on rt 
> kernels and had latency spikes from that.
>
>
> /Qoute
> (I believe you wrote that ?)

Yes. That's still true and that's one reason to not use it.

-Andi
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