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Date: Thu, 4 Sep 2014 14:46:56 +0530 From: Viresh Kumar <viresh.kumar@...aro.org> To: Preeti U Murthy <preeti@...ux.vnet.ibm.com> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Dirk Brandewie <dirk.brandewie@...il.com>, Dirk Brandewie <dirk.j.brandewie@...el.com>, Linux PM list <linux-pm@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Patrick Marlier <patrick.marlier@...il.com> Subject: Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq_driver interface. On 4 September 2014 14:40, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote: > cpufreq: Allow stop CPU callback to be used by all cpufreq drivers > > Commit 367dc4aa introduced the stop CPU callback for intel_pstate > drivers. During the CPU_DOWN_PREPARE stage, this callback is invoked > so that drivers can take some action on the pstate of the cpu > before it is taken offline. This callback was assumed to be useful > only for those drivers which have implemented the set_policy CPU > callback because they have no other way to take action about the > cpufreq of a CPU which is being hotplugged out except in the exit > callback which is called very late in the offline process. > > The drivers which implement the target/target_index callbacks were > expected to take care of requirements like the ones that commit > 367dc4aa addresses in the GOV_STOP notification event. But there > are disadvantages to restricting the usage of stop CPU callback > to cpufreq drivers that implement the set_policy callbacks and who > want to take explicit action on the setting the cpufreq during a > hotplug operation. > > 1.GOV_STOP gets called for every CPU offline and drivers would usually > want to take action when the last cpu in the policy->cpus mask > is taken offline. As long as there is more than one cpu in the > policy->cpus mask, cpufreq core itself makes sure that the freq > for the other cpus in this mask is set according to the maximum load. > This is sensible and drivers which implement the target_index callback > would mostly not want to modify that. However the cpufreq core leaves a > loose end when the cpu in the policy->cpus mask is the last one to go offline; > it does nothing explicit to the frequency of the core. Drivers may need > a way to take some action here and stop CPU callback mechanism is the > best way to do it today. > > 2.We cannot implement driver specific actions in the GOV_STOP mechanism. > So we will need another driver callback which is invoked from here which is > unnecessary. > > Therefore this patch extends the usage of stop CPU callback to be used > by all cpufreq drivers as long as they have this callback implemented > and irrespective of whether they are set_policy/target_index drivers. > The assumption is if the drivers find the GOV_STOP path to be a suitable > way of implementing what they want to do with the freq of the cpu > going offine,they will not implement the stop CPU callback at all. > > Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com> > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index d9fdedd..6463f35 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1380,7 +1380,7 @@ static int __cpufreq_remove_dev_prepare(struct device *dev, > if (!cpufreq_suspended) > pr_debug("%s: policy Kobject moved to cpu: %d from: %d\n", > __func__, new_cpu, cpu); > - } else if (cpufreq_driver->stop_cpu && cpufreq_driver->setpolicy) { > + } else if (cpufreq_driver->stop_cpu) { > cpufreq_driver->stop_cpu(policy); > } Rafael explicitly said earlier that he want to see a separate callback for ->target() drivers, don't know why.. It looks fine to me though. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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