Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

Florian Mickler
2010-06-04T13:09:21Z

On Thu, 3 Jun 2010 21:07:07 -0700
Arve Hjønnevåg <arve@android.com> wrote:

> On Thu, Jun 3, 2010 at 2:05 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > On Thursday 03 June 2010, James Bottomley wrote:
> >> On Thu, 2010-06-03 at 00:10 -0700, Arve Hjønnevåg wrote:
> >> > A request update then becomes something like this:
> >> >   if on primary list {
> >> >     unlink from primary list
> >> >     if secondary list is not empty
> >> >       get next secondary entry and add in same spot on primary list
> >> >   }
> >> >   unlink from secondary list
> >> >   find new spot on primary list
> >> >   if already there
> >> >     add to secondary list
> >> >   else
> >> >     add to primary list
> >>
> >> This is just reinventing hash bucketed lists.  To get the benefits, all
> >> we do is implement an N state constraint as backed by an N bucketed hash
> >> list, which the kernel already has all the internal mechanics for.
> >
> > Agreed.
> >
>
> No, a hash is used for quick lookup of a specific value, not to find
> an extreme value. It is however extremely similar to plists. The only
> difference is that plists link all the secondary lists together. If we
> want to have constraints that autoexpire, then keeping the secondary
> lists separate allows the same optimization as I did for
> wakelock/suspend_blocker timeouts where no timer is active if an
> (equal or stricter) non-expiring constraint is active.

Can you give an example for the optimization or elaborate about the
negative effect of linking the secondary lists together? I don't
understand right now.

Would be hlist from list.h better? (I think that is what James is
referring to?) That is a (single-linked-)list of double-linked-lists.

Cheers,
Flo