linux-kernel - Re: [RFC] ata port runtime pm

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Date:	Fri, 28 Oct 2011 13:36:34 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Jeff Garzik <jgarzik@...ox.com>
Cc:	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Priyanka Gupta <ankaguptaca@...il.com>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	"Huang, Ying" <ying.huang@...el.com>
Subject: Re: [RFC] ata port runtime pm

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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