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

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Date:	Fri, 28 Oct 2011 19:31:54 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Jeff Garzik <jgarzik@...ox.com>,
	"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>,
	Priyanka Gupta <ankaguptaca@...il.com>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [RFC] ata port runtime pm

Please CC PM-related patches to linux-pm@...r.kernel.org (now added).

Thanks,
Rafael


On Friday, October 28, 2011, Lin Ming wrote:
> 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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