Re: [PATCH v2] cpuidle: ladder: Add per CPU PM QoS resume latency support

[Ramesh Thomas <ramesh.thomas@intel.com>]

On 2017-10-27 at 09:59:38 +0200, Rafael J. Wysocki wrote:
> On Fri, Oct 27, 2017 at 4:01 AM, Ramesh Thomas <ramesh.thomas@intel.com> wrote:
> > Individual CPUs may have special requirements to not enter
> > deep idle states. For example, a CPU running real time
> > applications would not want to enter deep idle states to
> > avoid latency impacts. At the same time other CPUs that
> > do not have such a requirement could allow deep idle
> > states to save power.
> >
> > This was already implemented in the menu governor.
> > Implementing similar changes in the ladder governor which
> > gets selected when CONFIG_NO_HZ and CONFIG_NO_HZ_IDLE are not
> > set. Refer following commits for the menu governor changes.
> >
> > commit 9908859acaa9 ("cpuidle/menu: add per CPU PM QoS resume
> > latency consideration")
> > commit 6dbf5cea05a7 ("cpuidle: menu: Avoid taking spinlock for
> > accessing QoS values")
> >
> > Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>
> > ---
> >
> > v2:
> >   - use PM_QOS_RESUME_LATENCY_NO_CONSTRAINT for "no constraint" value
> >   Should be applied over https://patchwork.kernel.org/patch/10024157/
> >
> >  drivers/cpuidle/governors/ladder.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
> > index ce1a2ff..1ad8745 100644
> > --- a/drivers/cpuidle/governors/ladder.c
> > +++ b/drivers/cpuidle/governors/ladder.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/pm_qos.h>
> >  #include <linux/jiffies.h>
> >  #include <linux/tick.h>
> > +#include <linux/cpu.h>
> >
> >  #include <asm/io.h>
> >  #include <linux/uaccess.h>
> > @@ -67,10 +68,16 @@ static int ladder_select_state(struct cpuidle_driver *drv,
> >                                 struct cpuidle_device *dev)
> >  {
> >         struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
> > +       struct device *device = get_cpu_device(dev->cpu);
> >         struct ladder_device_state *last_state;
> >         int last_residency, last_idx = ldev->last_state_idx;
> >         int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
> >         int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
> > +       int resume_latency = dev_pm_qos_raw_read_value(device);
> > +
> > +       if (resume_latency < latency_req &&
> > +           resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> > +               latency_req = resume_latency;
> >
> >         /* Special case when user has set very strict latency requirement */
> >         if (unlikely(latency_req == 0)) {
> > --
> > 2.7.4
> >
> 
> Looks good to me.
> 
> I'll queue it up if nobody objects.
> 

Hi Rafael,

This patch would apply as is over your new PM QoS changes. If you need me
to repost please let me know.

Thanks,
Ramesh