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Re: [PATCH 2.5] SGI O2 framebuffer driver

To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH 2.5] SGI O2 framebuffer driver
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 12 Dec 2002 13:20:22 +0100
Cc: Vivien Chappelier <vivienc@nerim.net>, linux-mips@linux-mips.org, Ilya Volynets <ilya@theIlya.com>
In-reply-to: <1039697045.21231.13.camel@irongate.swansea.linux.org.uk>; from alan@lxorguk.ukuu.org.uk on Thu, Dec 12, 2002 at 12:44:05PM +0000
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <Pine.LNX.4.21.0212120004330.2300-100000@melkor> <1039656676.18587.63.camel@irongate.swansea.linux.org.uk> <20021212033307.C22987@linux-mips.org> <1039697045.21231.13.camel@irongate.swansea.linux.org.uk>
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On Thu, Dec 12, 2002 at 12:44:05PM +0000, Alan Cox wrote:

> > The O2 is non-cache coherent.  So with the fairly large write-back second
> > level caches enabled frame buffer write could potencially be delayed
> > indefinately but in any case quite long.  Frame buffers are usually only
> 
> You can flush the frame buffer pages that were touched at the end of an
> operation though

Flushes are very expensive operations, on the order of 16 cycles per
cacheline plus memory delay.  So why using them when just using the right
cache mode does the right thing already.

  Ralf

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