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    SubjectRe: submit_bh leaves interrupts on upon return
    Jens Axboe wrote:

    >On Thu, Jun 03 2004, Jeff V. Merkey wrote:
    >
    >
    >>Jens Axboe wrote:
    >>
    >>
    >>
    >>>Submitting large numbers of buffer_heads from b_end_io is _nasty_, 2.4
    >>>io scheduler runtime isn't exactly world champion and you are doing this
    >>>at hard irq time. Not a good idea. Definitely not the true path to
    >>>performance, unless you don't care about anything else in the system.
    >>>
    >>>At least in 2.6 you have a much faster io scheduler and the additionally
    >>>large bio, so you wont spend nearly as much time there if you are
    >>>clever. You still need process context, though, that hasn't changed.
    >>>
    >>>
    >>>
    >>>
    >>>
    >>Sounds like I need to move to 2.6. I noticed the elevator is coalescing
    >>quite well, and since I am posting mostly continguous runs of sectors,
    >>what ends up at the adapter level would probably not change much much
    >>between 2.4 and 2.6 since I am maxing out the driver request queues as
    >>it is (255 pending requests of 32 scatter/gather elements of 256 sector
    >>runs). 2.6 might help but I suspect it will only help alleviate the
    >>submission overhead, and not make much difference on performance since
    >>the 3Ware card does have an upward limit on outstanding I/O requests.
    >>
    >>
    >
    >That's correct, it just helps you diminish the submission overhead by
    >pushing down 256 sector entities in one go. So as long as you're io
    >bound it won't give you better io performance, of course. If you are
    >doing 400MiB/sec it should help you out, though.
    >
    >
    >
    I'll give it a try n 2.6.

    :-)

    Jeff

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