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Re: SGI IP28 support

To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Subject: Re: SGI IP28 support
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 27 Nov 2007 14:13:41 +0000
Cc: linux-mips@linux-mips.org
In-reply-to: <20071126223814.GA21339@alpha.franken.de>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20071126223814.GA21339@alpha.franken.de>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.17 (2007-11-01)
On Mon, Nov 26, 2007 at 11:38:14PM +0100, Thomas Bogendoerfer wrote:

> I finally cleaned up Peter Fuerst's IP28 patches and solved some of
> the IP28 issues in an IMHO more eye-friendly way (no ip26ucmem).
> My IP28 boots with these patches from an Debian sarge NFS root and
> is able to dd data from the harddrive. I'm going to send this patches
> to this list and the subsystem maintainers.
> 
> There is one change missing to get a working SCSI driver, because
> a proper fix will be done in 2.6.25. The quick&dirty workaround is
> below. The workaround makes sure that the sense_buffer lives in
> its own cache line by aligning and extendin it.
> 
> The patch "Use real cache invalidate" still contains one problem.
> It will not flush the cache correctly, if the given size is bigger
> than the second level cache. The problem is, that there is no index
> invalidate cache operation available. I have two ideas to solve that.
> One is to always do a range invalidate (maybe just by using this only
> for R10k machines, which usually have quite big caches) or scan through
> the cache and use the tag informations to do hit invalidate. If anybody
> has a better idea please speak up :-)

A while ago I instrumented the cacheflushing functions to get a histogram
of cacheflush sizes.  I was surprised to find no flushes larger than 64K
even though I did that experiment on an Origin with a large RAID array
copying huge amounts of data with reads and writes of several MB.  So as
long as that finding holds your code will work.

  Ralf

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