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    SubjectRe: [PATCH 33/35] libata: take advantage of cmwq and remove concurrency limitations
    On 06/28/2010 05:04 PM, Tejun Heo wrote:
    > libata has two concurrency related limitations.
    >
    > a. ata_wq which is used for polling PIO has single thread per CPU. If
    > there are multiple devices doing polling PIO on the same CPU, they
    > can't be executed simultaneously.
    >
    > b. ata_aux_wq which is used for SCSI probing has single thread. In
    > cases where SCSI probing is stalled for extended period of time
    > which is possible for ATAPI devices, this will stall all probing.
    >
    > #a is solved by increasing maximum concurrency of ata_wq. Please note
    > that polling PIO might be used under allocation path and thus needs to
    > be served by a separate wq with a rescuer.
    >
    > #b is solved by using the default wq instead and achieving exclusion
    > via per-port mutex.
    >
    > Signed-off-by: Tejun Heo<tj@kernel.org>
    > Cc: Jeff Garzik<jgarzik@pobox.com>

    Acked-by: Jeff Garzik <jgarzik@redhat.com>




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