On Thu, 2012-09-13 at 16:49 +0800, Aaron Lu wrote: > On 09/13/2012 04:37 PM, James Bottomley wrote: > > On Thu, 2012-09-13 at 16:23 +0800, Aaron Lu wrote: > >> On 09/13/2012 04:14 PM, James Bottomley wrote: > >>> On Thu, 2012-09-13 at 15:40 +0800, Aaron Lu wrote: > >>>> The ready_to_power_off flag is used to give indication to ATA layer > >>>> if this device's power can be removed when runtime suspended. > >>>> > >>>> This flag is determined by individual SCSI driver like sr, sd. > >>>> > >>>> This flag is introduced to support zero power ODD. When ODD > >>>> is runtime suspended, it may not be OK to remove its power. > >>>> > >>>> But for disk, it is always OK to be powered off, so set this flag. > >>> > >>> It is? I may have missed this, but where do you flush the cache of write > >>> back cache devices you're about to power off? > >> > >> I suppose that is handled in sd_suspend callback, the power off happens > >> after a device is runtime suspended. > > > > Well that would mean something is wrong somewhere: For runtime power > > management using idle timers and forced standby, there's no need to > > The current mechanism for scsi disk runtime pm is based on open/close. > If there is some process opened this block device, it will be in active > state; only when all opened session exited, it will enter runtime > suspend state. A mounted disk is open for the period of the mount. I thought the use case for runtime PM was the laptop one but most laptops have a single device to use as root, so if you never use runtime PM on an open device, you never use it on 99% of our target systems ... doesn't that make the feature a bit useless? > > flush the cache (if the drive goes into standby on its own as a result > > of an idle timeout, the cache will never flush). The cache needs to > > flush before we power off the device: that's before the system goes into > > S3, or now before you power it off at runtime. Flushing the cache on > > runtime transitions to standby will likely cause performance problems > > since that happens quite often. > > As explained above, it didn't happen that often, especially for user who > has only one disk, the disk will be mounted, which makes it never be > able to enter runtime suspend state. So what's the target audience for the feature. If it isn't laptops or standard desktops, is it the enterprise? James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
