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Re: shared memory

To: Tom Appermont <tea@sonycom.com>
Subject: Re: shared memory
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Wed, 29 Aug 2001 05:37:48 +0200
Cc: linux-mips@oss.sgi.com
In-reply-to: <20010828191725.A1221@sonycom.com>; from tea@sonycom.com on Tue, Aug 28, 2001 at 07:17:25PM +0200
References: <20010828191725.A1221@sonycom.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Tue, Aug 28, 2001 at 07:17:25PM +0200, Tom Appermont wrote:

> While this works as expected on PC, it does not at all work as
> expected on my mips platform (R5231): What is written in user
> space is not immediately visible in kernel space. This is with
> very recent kernel sources (2.4.8) but the same problem exists
> with an older (2.4.5) kernel.
> 
> There have been a few mails about mmap() problems in the last 
> couple of months, but with very little interesting response. Is 
> this a known problem or am I stupidly overlooking something?

This is a different problem - and it's one caused by your code.  You're
missing the necessary cache flushes in the kernel code.  Using
_CACHE_UNCACHED is slow and breaks SMP.

 Ralf

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