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

mark gross
2010-06-01T14:05:07Z

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@gmail.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@rowland.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@mickler.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@mickler.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
>