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List:       linux-arm-kernel
Subject:    Re: perfomance of copy_to/from_user
From:       Nicolas Pitre <nico () cam ! org>
Date:       2004-10-06 16:28:24
Message-ID: Pine.LNX.4.61.0410061225490.25631 () xanadu ! home
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On Wed, 6 Oct 2004, Thomas Wöckinger wrote:

> Hi!
> 
> I have some performance Problems using copy_to_user or copy_from_user. I can 
> only transfer about 22,5 MB/s from or to userspace
> 
> I am using an Intel Xscale processor running on 500MHz pluged into idxp425 
> development board. An DSP card (pluged into PCI slot) is writing directly 
> into a 256K kernel space buffer.
> 
> the kernel version is 2.6.8.1
> 
> My first question is: can i speed up the copy_to/from_user?

Hardly.

> if not, is it possible on an idxp425 board to access the whole memory 
> directly, so that i can write to the userspace buffer without using the 
> xscale.

It is possible for you to mmap() the 256k kernel buffer into user space 
and avoid copying the data entirely.


Nicolas

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