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    SubjectRe: [PATCH] block: Make rq_affinity = 1 work as expected.
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    On Thu, Aug 4, 2011 at 10:12 PM, Shaohua Li <shli@kernel.org> wrote:
    > 2011/8/5 Tao Ma <tm@tao.ma>:
    >> From: Tao Ma <boyu.mt@taobao.com>
    >>
    >> Commit 5757a6d76c introduced a new rq_affinity = 2 so as to make
    >> the request completed in the __make_request cpu. But it makes the
    >> old rq_affinity = 1 not work any more. The root cause is that
    >> if the 'cpu' and 'req->cpu' is in the same group and cpu != req->cpu,
    >> ccpu will be the same as group_cpu, so the completion will be
    >> excuted in the 'cpu' not 'group_cpu'.
    >>
    >> This patch fix problem by simpling removing group_cpu and the codes
    >> are more explicit now. If ccpu == cpu, we complete in cpu, otherwise
    >> we raise_blk_irq to ccpu.
    > good catch. This changed old behavior and can cause more lock contention.
    > and if user doesn't care about lock contention, he can use rq_affinity = 2
    >

    Indeed it does change behavior of rq_affinity=1, apologies.

    Reviewed-by: Dan Williams <dan.j.williams@intel.com>


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