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    SubjectRe: [PATCH 2/4]: powerpc/cell spidernet low watermark patch.
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    On Fri, 2006-08-11 at 12:08 -0500, Linas Vepstas wrote:
    >
    > Implement basic low-watermark support for the transmit queue.
    >
    > The basic idea of a low-watermark interrupt is as follows.
    > The device driver queues up a bunch of packets for the hardware
    > to transmit, and then kicks he hardware to get it started.
    > As the hardware drains the queue of pending, untransmitted
    > packets, the device driver will want to know when the queue
    > is almost empty, so that it can queue some more packets.
    >
    > This is accomplished by setting the DESCR_TXDESFLG flag in
    > one of the packets. When the hardware sees this flag, it will
    > interrupt the device driver. Because this flag is on a fixed
    > packet, rather than at fixed location in the queue, the
    > code below needs to move the flag as more packets are
    > queued up. This implementation attempts to keep te flag
    > at about 3/4's of the way into the queue.
    >
    > This patch boosts driver performance from about
    > 300-400Mbps for 1500 byte packets, to about 710-740Mbps.

    Sounds good (without actually looking at the code though :), that was a
    long required improvement to that driver. Also, we should probably look
    into using NAPI polling for tx completion queue as well, no ?

    Cheers,
    Ben.


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