linux-kernel - Re: [PATCH] x86: copy_oldmem_page using cached addressing

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Message-ID: <87eid4vx7p.fsf@basil.nowhere.org>
Date:	Wed, 08 Sep 2010 21:42:18 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Cliff Wickman <public-cpw-sJ/iWh9BUns@...ne.gmane.org>
Cc:	public-kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@...ne.gmane.org,
	public-mingo-X9Un+BFzKDI@...ne.gmane.org,
	public-linux-kernel-u79uwXL29TY76Z2rM5mHXA@...ne.gmane.org
Subject: Re: [PATCH] x86: copy_oldmem_page using cached addressing



Cliff Wickman <cpw-sJ/iWh9BUns@...lic.gmane.org> writes:

> From: Cliff Wickman <cpw-sJ/iWh9BUns@...lic.gmane.org>
>
> The copy of /proc/vmcore to a user buffer proceeds much faster
> if the kernel addresses memory as cached.
>
> With this patch we have seen an increase in transfer rate from less than
> 15MB/s to 80-460MB/s, depending on size of the transfer.  This makes
> a big difference in time needed to save a system dump.
>
> (Does anyone know of a reason why copy_oldmem_page() would need
>  to use uncached addresses?)
>
> Diffed against 2.6.36-rc3

I had a similar patch somewhere in my private kernels,
yes it's a big win. I think it was simply a bug that was added
when ioremap was changed to default to uncached.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.

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