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

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Message-ID: <1275578992.5914.146.camel@mulgrave.site>
Date:	Thu, 03 Jun 2010 10:29:52 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Florian Mickler <florian@...kler.org>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	markgross@...gnar.org, 640e9920@...il.com,
	Peter Zijlstra <peterz@...radead.org>,
	Brian Swetland <swetland@...gle.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Thu, 2010-06-03 at 17:17 +0200, Florian Mickler wrote:
> On Thu, 03 Jun 2010 09:36:34 -0500
> James Bottomley <James.Bottomley@...e.de> wrote:
> 
> > On Thu, 2010-06-03 at 00:10 -0700, Arve Hjønnevåg wrote:
> > > On Wed, Jun 2, 2010 at 10:40 PM, mark gross <640e9920@...il.com> wrote:
> > > > On Wed, Jun 02, 2010 at 09:54:15PM -0700, Brian Swetland wrote:
> > > >> On Wed, Jun 2, 2010 at 8:18 PM, mark gross <640e9920@...il.com> wrote:
> > > >> > On Wed, Jun 02, 2010 at 02:58:30PM -0700, Arve Hjønnevåg wrote:
> > > >> >>
> > > >> >> The list is not short. You have all the inactive and active
> > > >> >> constraints on the same list. If you change it to a two level list
> > > >> >> though, the list of unique values (which is the list you have to walk)
> > > >> >> may be short enough for a tree to be overkill.
> > > >> >
> > > >> > what have you seen in practice from the wake-lock stats?
> > > >> >
> > > >> > I'm having a hard time seeing where you could get more than just a
> > > >> > handfull.  However; one could go to a dual list (like the scheduler) and
> > > >> > move inactive nodes from an active to inactive list, or we could simply
> > > >> > remove them from the list uppon inactivity.  which would would well
> > > >> > after I change the api to have the client allocate the memory for the
> > > >> > nodes...  BUT, if your moving things in and out of a list a lot, I'm not
> > > >> > sure the break even point where changing the structure helps.
> > > >> >
> > > >> > We'll need to try it.
> > > >> >
> > > >> > I think we will almost never see more than 10 list elements.
> > > >> >
> > > >> > --mgross
> > > >> >
> > > >> >
> > > >>
> > > >> I see about 80 (based on the batteryinfo dump) on my Nexus One
> > > >> (QSD8250, Android Froyo):
> > > >
> > > > shucks.
> > > >
> > > > well I think for a pm_qos class that has boolean dynamic range we can
> > > > get away with not walking the list on every request update.  we can use
> > > > a counter, and the list will be for mostly for stats.
> > > >
> > > 
> > > Did you give any thought to my suggestion to only use one entry per
> > > unique value on the first level list and then use secondary lists of
> > > identical values. That way if you only have two constraints values the
> > > list you have to walk when updating a request will never have more
> > > than two entries regardless of how many total request you have.
> > > 
> > > 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.
> > 
> > James
> >
> 
> http://www.itl.nist.gov/div897/sqg/dads/HTML/priorityque.html
> 
> So no reinvention. Just using a common scheme. 

By reinvention I meant open coding a common pattern for which the kernel
already has an API.  (Whether we go with hash buckets or plists).

James


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