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

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Date:	Tue, 1 Jun 2010 07:05:19 -0700
From:	mark gross <640e9920@...il.com>
To:	Florian Mickler <florian@...kler.org>
Cc:	markgross@...gnar.org, 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 Tue, Jun 01, 2010 at 09:07:37AM +0200, Florian Mickler wrote:
> 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);
> +}
> +

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!

thanks!

--mgross

>  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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