On 14-03-19, 10:28, Rafael J. Wysocki wrote: > On Thu, Mar 14, 2019 at 7:43 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > > > > Currently we call the cpufreq transition notifiers once for each CPU of > > the policy->cpus cpumask, which isn't that efficient. > > Why isn't it efficient? > > Transitions are per-policy anyway, so if something needs to be done > for each CPU in the policy, it doesn't matter too much which part of > the code carries out the iteration. Even if per-cpu iteration has to be done at some place, we are avoiding function calls here and the code/locking in the notifier layer as well. Will get more such info into changelog. > I guess some notifiers need to know what other CPUs there are in the > policy? If so, then why? You mean about the offline CPUs? I mentioned the rationale in 1/7. It is to avoid bugs where we may end up using a stale value if the CPUs are offlined/onlined regularly. > > This patchset tries to simplify that by adding another field in struct cpufreq_freqs, > > cpus, so the callback has all the information available with a single > > call for each policy. > > Well, you can argue that the core is simplified by it somewhat, but > the notifiers aren't. They actually get more complex, conceptually > too, because they now need to worry about offline vs online CPUs etc. 24 different parts of the kernel register for transition notifiers and only 5 required update here, the other 19 don't need to do per-cpu stuff and they also get benefited by this work. Those routines will get called only once now, instead of once per every CPU of the policy. > Also I wonder why you decided to pass a cpumask in freqs instead of > just passing a policy pointer. If you change things from per-CPU to > per-policy, passing the whole policy seems more natural. I did that because they don't need to use the other fields of the policy today and that doesn't look likely in near future as well. I can do that if you want, but not sure why more information should be provided than required. -- viresh
