Re: MSI to memory?

From: Roland Dreier (roland_at_topspin.com)
Date: 07/07/04

  • Next message: Zwane Mwaikambo: "Re: MSI to memory?" 
    To: Helge Hafting <helge.hafting@hist.no>
Date:	Wed, 07 Jul 2004 09:59:14 -0700

        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>
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  • Next message: Zwane Mwaikambo: "Re: MSI to memory?"

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