Re: syncing the disks when entering sleep

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Friday 22 January 2010, Nigel Cunningham wrote:
> Hi.
> 
> Rafael J. Wysocki wrote:
> > On Friday 22 January 2010, Leisner, Martin wrote:
> >> I noticed when we enter sleep states, it seems there's always a
> >> sys_sync given.
> >>
> >> When having an embedded system doing WOL (already in laptop mode to
> >> cache
> >> all the writes), it reasonable to wake up dozens of times of day and
> >> quickly go back to sleep.  If the disk is not spun up,
> >> and there's some work to be done, won't the sys_sync spin up the disk
> >> before going to sleep?
> >>
> >> It would be good to have a knob (in /sys) you can tweak from usespace to
> >>
> >> configure the behavior of whether you want to do a sync when entering
> >> sleep.
> >>
> >> The ideal behavior would be:
> >>
> >>     if(disk is spun up)
> >>         then let the sync happen
> > 
> > I'm not against that.  Patch welcome. :-)
> 
> Oooh. I am. That's providing potential for unpredictable behaviour. Much
> better IMO would be providing a tuning know that explicitly and
> unconditionally disables syncing.

You're right, sorry.

Yes, a knob that disables syncing unconditionally was the thing I was thinking
about.

Rafael