On Thu, 24 Nov 2011, Tejun Heo wrote:
> Hello,
>
> On Thu, Nov 24, 2011 at 2:54 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > Therefore, when entering the SUSPEND or HIBERNATE stages of system
> > sleep, we can skip the callback to the driver if the device is already
> > in runtime suspend. �When entering the FREEZE stage, however, we should
> > first issue a runtime resume. �The overhead of doing this is
> > negligible, because a suspended drive would be spun up during the THAW
> > stage of hibernation anyway.
>
> My brain is half fried at the moment so maybe you're saying the same
> thing, but I hope this is something simple. Like...
>
> /* for libata runtime suspend is equivalent to suspend */
> if (runtime suspended && target == SUSPEND) {
> yeah! skip drive pm ops;
> } else {
> end runtime pm;
> ask EH to enter target PM state;
> }
Almost. More like this:
/*
* sd is the only high-level SCSI driver to implement runtime
* PM, and sd treats runtime suspend, system suspend, and
* system hibernate identically (but not system freeze).
*/
if (runtime-suspended) {
if (target == SUSPEND || target == HIBERNATE)
return 0; /* already suspended */
/* wake up device so that FREEZE will succeed */
pm_runtime_resume();
}
tell device driver to enter target PM state
libata does not contain the SCSI device driver; it contains the host
driver.
> I really don't think we need to optimize this further than this.
The above has two lines (plus comments) of optimization. Okay?
Alan Stern
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