From: Helge Hafting <helge.hafting@hist.no>
To: Roland Dreier <roland@topspin.com>
Cc: Davide Rossetti <davide.rossetti@roma1.infn.it>,
linux-kernel@vger.kernel.org
Subject: Re: MSI to memory?
Date: Thu, 08 Jul 2004 11:03:24 +0200 [thread overview]
Message-ID: <40ED0DDC.20602@hist.no> (raw)
In-Reply-To: <52vfgzoisd.fsf@topspin.com>
Roland Dreier wrote:
> 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)
>
>
I see. Still, this should only be used when we expect a
short wait only, similiar to situations when we use a spinlock.
Otherwise, the cpu could be put to better use by scheduling.
Helge Hafting
next prev parent reply other threads:[~2004-07-08 9:00 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
2004-07-08 9:03 ` Helge Hafting [this message]
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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