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

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Message-ID: <AANLkTilSU79cnBODXFokzIPB1hRcZBxbwTgTQ59MeKcK@mail.gmail.com>
Date:	Wed, 2 Jun 2010 14:58:30 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	markgross@...gnar.org
Cc:	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)

2010/6/2 mark gross <640e9920@...il.com>:
> 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.
>

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.

-- 
Arve Hjønnevåg
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