Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH 1/3] pm/qos: allow state control of qos class | Date | Wed, 22 Jan 2014 00:15:44 +0100 |
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On Tuesday, January 21, 2014 02:10:42 PM Jacob Pan wrote: > On Thu, 16 Jan 2014 02:17:01 +0100 > "Rafael J. Wysocki" <rjw@rjwysocki.net> wrote: > > > On Wednesday, November 27, 2013 12:28:16 AM Rafael J. Wysocki wrote: > > > On 11/27/2013 12:20 AM, Jacob Pan wrote: > > > > When power capping or thermal control is needed, CPU QOS latency > > > > cannot be satisfied. This patch adds a state variable to indicate > > > > whether a QOS class (including all constraint requests) should be > > > > ignored. > > > > > > > > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com> > > > > > > Honestly, I don't like this. I know the motivation and what you're > > > trying to achieve, but I don't like the approach. > > > > > > I need to think a bit more about that. > > > > So the reason I don't like this patch is mainly because it affects > > all of the users of struct pm_qos_constraints and > > pm_qos_read_value(), which include device PM QoS among other things, > > but it only really needs to affect PM_QOS_CPU_DMA_LATENCY. > > > > I would add a special routine, say pm_qos_cpu_dma_latency(), for > > reading the current effective PM_QOS_CPU_DMA_LATENCY constraint and > > checking whether or not it should be ignored. Then, I'd make cpuidle > > use that. > > > Agreed, it was a little too broad. I will send an updated patch soon. > > Alternatively, can we add a special check for ignored system wide QOS > class in: > int pm_qos_request(int pm_qos_class) > > i.e. > diff --git a/kernel/power/qos.c b/kernel/power/qos.c > index 8dff9b4..9342da4 100644 > --- a/kernel/power/qos.c > +++ b/kernel/power/qos.c > @@ -286,10 +286,28 @@ bool pm_qos_update_flags(struct pm_qos_flags *pqf, > */ > int pm_qos_request(int pm_qos_class) > { > - return pm_qos_read_value(pm_qos_array[pm_qos_class]->constraints); > + struct pm_qos_constraints *c; > + > + c = pm_qos_array[pm_qos_class]->constraints; > + if (c->state == PM_QOS_CONSTRAINT_IGNORED) > + return PM_QOS_DEFAULT_VALUE; > + return pm_qos_read_value(c); > > > Then we don't have to add a special routine just for CPU_DMA_LATENCY > class. It does not affect other system wide QOS classes unless the > state is set to be ignored.
Yes, but then the check has to be done regardless which is slightly inefficient and I'm not sure if we need/want a mechanism to set "ignored" for all classes.
It actually is specific to CPU in practice, so I'd prefer to make it specific in the code as well.
Thanks, Rafael
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