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

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Date:	Wed, 2 Jun 2010 06:39:10 -0700
From:	mark gross <640e9920@...il.com>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	markgross@...gnar.org, Florian Mickler <florian@...kler.org>,
	640e9920@...il.com, "Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Brian Swetland <swetland@...gle.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Tue, Jun 01, 2010 at 08:50:02PM -0700, Arve Hjønnevåg wrote:
> On Tue, Jun 1, 2010 at 7:05 AM, mark gross <640e9920@...il.com> wrote:
> > On Tue, Jun 01, 2010 at 09:07:37AM +0200, Florian Mickler wrote:
> ...
> >> +static void update_target_val(int pm_qos_class, s32 val)
> >> +{
> >> +     s32 extreme_value;
> >> +     s32 new_value;
> >> +     extreme_value = atomic_read(&pm_qos_array[pm_qos_class]->target_value);
> >> +     new_value = pm_qos_array[pm_qos_class]->comparitor(val,extreme_value);
> >> +     if (extreme_value != new_value)
> >> +             atomic_set(&pm_qos_array[pm_qos_class]->target_value,new_value);
> >> +}
> >> +
> >
> > Only works 1/2 the time, but I like the idea!
> > It fails to get the righ answer when constraints are reduced.  But, this
> > idea is a good improvement i'll roll into the next pm_qos update!
> >
> 
> I think it would be a better idea to track your constraints with a
> sorted data structure. That way you can to better than O(n) for both
> directions. If you have a lot of constraints with the same value, it
> may even be worthwhile to have a two stage structure where for
> instance you use a rbtree for the unique values and list for identical
> constraints.

I don't agree, we went through this tree vrs list discussion a few times
before in other areas of the kernel.  Wherever the list tended to be
short, a simple list wins.  However; we can try it, after we have some
metrics and stress test cases identified we can measure its effectivenes
against.

--mgross

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