From: Roland Dreier <roland@topspin.com>
To: Helge Hafting <helge.hafting@hist.no>
Cc: Davide Rossetti <davide.rossetti@roma1.infn.it>,
linux-kernel@vger.kernel.org
Subject: Re: MSI to memory?
Date: Wed, 07 Jul 2004 09:59:14 -0700 [thread overview]
Message-ID: <52vfgzoisd.fsf@topspin.com> (raw)
In-Reply-To: <40EBF07B.8040003@hist.no> (Helge Hafting's message of "Wed, 07 Jul 2004 14:45:47 +0200")
Helge> Won't that put a bad load on the bus? Someone else might
Helge> need it: * Another cpu in a smp system * Any device doing
Helge> bus-master transfers, even in a UP system
Actually with MSI, the PCI device writes directly to a host address.
In the proposed usage in this mail thread, the address is in host
memory, so there's no bus load to poll the memory. Presumably the
memory will be pulled into cache for the duration of the poll loop, so
there's not even any memory bandwidth consumed. (Of course this only
works on an architecture where PCI DMA is cache coherent)
- Roland
Date: Wed, 07 Jul 2004 09:59:04 -0700
In-Reply-To: <40EBF07B.8040003@hist.no> (Helge Hafting's message of "Wed, 07 Jul 2004 14:45:47 +0200")
Message-ID: <52wu1foisn.fsf@topspin.com>
User-Agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Security Through Obscurity, linux)
next prev parent reply other threads:[~2004-07-07 17:00 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-01 18:15 MSI to memory? Bjorn Helgaas
2004-07-01 18:53 ` Rajesh Shah
2004-07-02 15:51 ` Bjorn Helgaas
2004-07-07 12:31 ` Davide Rossetti
2004-07-07 12:45 ` Helge Hafting
2004-07-07 16:59 ` Roland Dreier [this message]
2004-07-08 9:03 ` Helge Hafting
2004-07-07 17:04 ` Zwane Mwaikambo
2004-07-07 13:15 ` Richard B. Johnson
2004-07-07 17:13 ` Rajesh Shah
2004-07-02 16:04 ` Roland Dreier
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