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To: G?rard Roudier <groudier@club-internet.fr>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Ion Badulescu <ionut@cs.columbia.edu>,
        Alan Cox <alan@redhat.com>, Donald Becker <becker@scyld.com>,
        Jeff Garzik <jgarzik@mandrakesoft.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] starfire reads irq before pci_enable_device.
In-Reply-To: <Pine.LNX.4.10.10102100932360.1117-100000@linux.local>
From: Jes Sorensen <jes@linuxcare.com>
Date: 12 Feb 2001 20:01:48 +0100
In-Reply-To: G?rard Roudier's message of "Sat, 10 Feb 2001 09:48:41 +0100 (CET)"
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>>>>> "G?rard" == G?rard Roudier <groudier@club-internet.fr> writes:

G?rard> On Fri, 9 Feb 2001, Alan Cox wrote:

>> DMA to main memory normally invalidates those lines in the CPU
>> cache rather than the cache snooping and updating its view of them.

G?rard> In PCI, it is the Memory Write and Invalidate PCI transaction
G?rard> that is intended to allow core-logics to optimize DMA this
G?rard> way. For normal Memory Write PCI transactions or when the
G?rard> core-logic is aliasing MWI to MW, the snooping may well
G?rard> happen. All that stuff, very probably, varies a lot depending
G?rard> on the core-logic.

In fact one has to look out for this and disable the feature in some
cases. On the acenic not disabling Memory Write and Invalidate costs
~20% on performance on some systems.

Jes
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