linux-kernel - Re: howto use ioremap

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Message-ID: <4844395C.2010900@myri.com>
Date:	Mon, 02 Jun 2008 14:18:04 -0400
From:	Loic Prylli <loic@...i.com>
To:	Brice Goglin <brice@...i.com>
CC:	Arjan van de Ven <arjan@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
	"venkatesh.pallipadi@...el.com" <venkatesh.pallipadi@...el.com>
Subject: Re: howto use ioremap_wc?

On 06/02/2008 12:27 PM, Brice Goglin wrote:
> Arjan van de Ven wrote:
>   
>> Ok this leads to a question: since write combining is effectively an
>> extension (eg relaxation) to uncached, how much do you care if you
>> actually get uncached? Eg can you just use the "WC" function even for
>> the case where you get an uncached mapping ?
>>   
>>     
>
> WC is strictly required for our "wcfifo" path,




To be more accurate about the above statement, that codepath will still 
work correctly even if the mapping ends-up being uncached, but that 
could lead to a 16X slowdown on some machines, since that path was 
really designed for the WC case.


Anyway that codepath does not really matter as Brice mentioned 
afterwards :-)



>  but this path is actually
> not so important nowadays. It is disabled by default and might even be
> removed in the future. So, no, myri10ge itself does not really need to
> know whether the mapping is actually WC.
>   




Loic

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