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

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Message-ID: <20100601090737.4bc243d9@schatten.dmk.lab>
Date:	Tue, 1 Jun 2010 09:07:37 +0200
From:	Florian Mickler <florian@...kler.org>
To:	markgross@...gnar.org
Cc:	640e9920@...il.com, "Rafael J. Wysocki" <rjw@...k.pl>,
	Arve Hjønnevåg <arve@...roid.com>,
	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 Mon, 31 May 2010 16:26:17 -0700
mark gross <640e9920@...il.com> wrote:

> On Mon, May 31, 2010 at 11:38:55PM +0200, Rafael J. Wysocki wrote:
> > On Monday 31 May 2010, Arve Hjønnevåg wrote:
> > > 2010/5/29 Alan Stern <stern@...land.harvard.edu>:
> > > > On Sat, 29 May 2010, Arve Hjønnevåg wrote:
> > > >
> > > >> > In place of in-kernel suspend blockers, there will be a new type of QoS
> > > >> > constraint -- call it QOS_EVENTUALLY.  It's a very weak constraint,
> > > >> > compatible with all cpuidle modes in which runnable threads are allowed
> > > >> > to run (which is all of them), but not compatible with suspend.
> > > >> >
> > > >> This sound just like another API rename. It will work, but given that
> > > >> suspend blockers was the name least objectionable last time around,
> > > >> I'm not sure what this would solve.
> > > >
> > > > It's not just a rename.  By changing this into a QoS constraint, we
> > > > make it more generally useful.  Instead of standing on its own, it
> > > > becomes part of the PM-QOS framework.
> > > >
> > > 
> > > We cannot use the existing pm-qos framework. It is not safe to call
> > > from atomic context.
> > 
> > We've just merged a patch that fixed that if I'm not mistaken.  Mark, did your
> > PM QoS update fix that?
> >
> 
> I'm pretty sure it can be called in atomic context, and if its not I'm
> sure we can fix that.  It can be called in atomic context.  I don't
> think it was ever a problem to call it in atomic context.  The problem it
> had was that crappy list of string compares.  Thats been fixed.
> 
> --mgross
>  

Well, the register call uses kzalloc. Apart from that I
think we're good. 

The outstanding list traversals can be fixed also. (see below)

Cheers,
Flo

>From 66fdd76f8cc4be722dba3859ddadfe07e7a4b755 Mon Sep 17 00:00:00 2001
From: Florian Mickler <florian@...kler.org>
Date: Tue, 1 Jun 2010 09:04:26 +0200
Subject: [PATCH] pm_qos: remove unnecessary list-traversal

The new extreme_value is only depending on the old extreme_value and
the changing value.

Signed-off-by: Florian Mickler <florian@...kler.org>
---
 kernel/pm_qos_params.c |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
index f42d3f7..6618e2c 100644
--- a/kernel/pm_qos_params.c
+++ b/kernel/pm_qos_params.c
@@ -136,6 +136,16 @@ static s32 min_compare(s32 v1, s32 v2)
 }
 
 
+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);
+}
+
 static void update_target(int pm_qos_class)
 {
 	s32 extreme_value;
@@ -227,8 +237,8 @@ struct pm_qos_request_list *pm_qos_add_request(int pm_qos_class, s32 value)
 		spin_lock_irqsave(&pm_qos_lock, flags);
 		list_add(&dep->list,
 			&pm_qos_array[pm_qos_class]->requests.list);
+		update_target_val(pm_qos_class,dep->value);
 		spin_unlock_irqrestore(&pm_qos_lock, flags);
-		update_target(pm_qos_class);
 	}
 
 	return dep;
@@ -249,23 +259,21 @@ void pm_qos_update_request(struct pm_qos_request_list *pm_qos_req,
 		s32 new_value)
 {
 	unsigned long flags;
-	int pending_update = 0;
 	s32 temp;
 
 	if (pm_qos_req) { /*guard against callers passing in null */
+		int target = pm_qos_req->pm_qos_class;
 		spin_lock_irqsave(&pm_qos_lock, flags);
 		if (new_value == PM_QOS_DEFAULT_VALUE)
-			temp = pm_qos_array[pm_qos_req->pm_qos_class]->default_value;
+			temp = pm_qos_array[target]->default_value;
 		else
 			temp = new_value;
 
 		if (temp != pm_qos_req->value) {
-			pending_update = 1;
 			pm_qos_req->value = temp;
+			update_target_val(target,temp);
 		}
 		spin_unlock_irqrestore(&pm_qos_lock, flags);
-		if (pending_update)
-			update_target(pm_qos_req->pm_qos_class);
 	}
 }
 EXPORT_SYMBOL_GPL(pm_qos_update_request);
-- 
1.7.1

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