linux-kernel - Re: Multiple MSI messages support

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Message-Id: <20071030.160221.27099706.davem@davemloft.net>
Date:	Tue, 30 Oct 2007 16:02:21 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	rdreier@...co.com
Cc:	jeff@...zik.org, shawnxjin@...il.com, linux-kernel@...r.kernel.org
Subject: Re: Multiple MSI messages support

From: Roland Dreier <rdreier@...co.com>
Date: Tue, 30 Oct 2007 15:51:08 -0700

> In fact at least IBM pSeries boxes seem to be able to use MSI to
> generate multiple interrupts from the same device -- BenH can probably
> give details.

Sparc64 PCI-E controllers can do this as well.

> For high-performance devices this is not really true.  The InfiniBand
> mthca driver can use MSI to get a single interrupt, or MSI-X to get
> different interrupts for different types of events.  MSI-X allows the
> read of the "interrupt cause register" to be avoided, and this ends up
> making a measurable performance difference for the fast path.
> 
> Also, obviously, having multiple interrupts means you can bind
> different interrupts to different CPUs, which will become very
> important if/when things like multi-queue NICs are supported.

Right, and this is used heavily in the NIU driver for example.
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