linux-kernel - Re: [PATCH] x86/smpboot: check if CLFLUSH is actually necessary

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Message-ID: <54DBE154.5040204@eng.utah.edu>
Date:	Wed, 11 Feb 2015 16:10:12 -0700
From:	Scotty Bauer <sbauer@....utah.edu>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org,
	x86@...nel.org, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/smpboot: check if CLFLUSH is actually necessary


On 02/11/2015 02:55 PM, H. Peter Anvin wrote:
> On 01/30/2015 01:26 PM, Scotty Bauer wrote:
>> mwait_play_dead previously issued a CLFLUSH to work around a bug on
>> some xeon processors. We can now determine if the CPU is a buggy CPU.
>> This patch checks if if we're on a buggy CPU which allows non-buggy
>> cpu's to eliminate the CLFLUSH.
> Here is my first question: does this matter at all?  Otherwise I don't
> see a point.
>
> 	-hpa
>
>
Do you get the same effect? Sure, but is the previous way the right way to do it? In my opinion no, but I'm not the one merging code its up to someone more experienced to determine if the change is warranted. The change is slightly faster on non-buggy cpu, but like you mention, is that relevant when the machine is going into idle?


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