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

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Message-ID: <4A698B3E.4020208@vmware.com>
Date:	Fri, 24 Jul 2009 12:21:50 +0200
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	"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

Andi Kleen wrote:
> Thomas Hellstrom <thellstrom@...are.com> writes:
>
>   
>> The current code uses wbinvd() when the area to flush is > 4MB. Although this
>> may be faster than using clflush() the effect of wbinvd() on irq latencies
>> may be catastrophical on systems with large caches. Therefore use clflush()
>>     
>
> may be? You seem to miss some hard data here.
>
>   
Admittedly.
However, the concept of flushing and invalidating the caches completely 
on systems with many
processors and huge caches when we intend to only flush only small piece 
of the cache also sounds like a big overkill.

Furthermore, since the wbinvd() has been introduced as an optimization 
of the general clflush() case, did somebody ever check the effects on 
systems with many processors and huge caches?

/Thomas

> -Andi
>
>   

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