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    SubjectRe: [RFC] ata port runtime pm
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    On Fri, 2011-10-28 at 11:37 +0800, Jeff Garzik wrote:
    > On 10/27/2011 11:21 PM, Lin Ming wrote:
    > > @@ -3208,6 +3209,11 @@ int ata_scsi_queuecmd(struct Scsi_Host *shost, struct scsi_cmnd *cmd)
    > >
    > > ap = ata_shost_to_port(shost);
    > >
    > > + if (pm_runtime_suspended(&ap->tdev))
    > > + pm_runtime_resume(&ap->tdev);
    > > + pm_runtime_mark_last_busy(&ap->tdev);
    > > + pm_request_autosuspend(&ap->tdev);
    > > +
    > > spin_lock_irqsave(ap->lock, irq_flags);
    > >
    >
    >
    > Putting this into the core command dispatch fast-path is rather
    > disappointing. That's at least one additional lock, plus some atomic
    > instructions and tests.

    Maybe move suspend request to the resume function, as below.

    static int ata_port_runtime_resume(struct device *dev)
    {
    struct ata_port *ap = to_ata_port(dev);
    int rc;

    rc = ata_port_request_pm(ap, PMSG_ON, ATA_EH_RESET,
    ATA_EHI_NO_AUTOPSY | ATA_EHI_QUIET, 1);

    pm_runtime_mark_last_busy(dev);
    pm_request_autosuspend(dev);

    return rc;
    }

    Then the fast-path looks like,

    @@ -3208,6 +3209,9 @@ int ata_scsi_queuecmd(struct Scsi_Host *shost,
    struct scsi_cmnd *cmd)

    ap = ata_shost_to_port(shost);

    + if (pm_runtime_suspended(&ap->tdev))
    + pm_runtime_resume(&ap->tdev);
    +
    spin_lock_irqsave(ap->lock, irq_flags);

    ata_scsi_dump_cdb(ap, cmd);
    What do you think?

    Thanks,
    Lin Ming



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