On 13 June 2013 14:31, Xiaoguang Chen <chenxg@xxxxxxxxxxx> wrote: > cpufreq governor stop and start should be kept in sequence. > If not, there will be unexpected behavior, for example: > > we have 4 cpus and policy->cpu=cpu0, cpu1/2/3 are linked to cpu0. > the normal sequence is as below: > > 1) Current governor is userspace, one application tries to set > governor to ondemand. it will call __cpufreq_set_policy in which it > will stop userspace governor and then start ondemand governor. > > 2) Current governor is userspace, now cpu0 hotplugs in cpu3, it will > call cpufreq_add_policy_cpu. on which it first stops userspace > governor, and then starts userspace governor. > > Now if the sequence of above two cases interleaves, it becames > below sequence: > > 1) application stops userspace governor > 2) hotplug stops userspace governor > 3) application starts ondemand governor > 4) hotplug starts a governor > > in step 4, hotplug is supposed to start userspace governor, but now > the governor has been changed by application to ondemand, so hotplug > starts ondemand governor again !!!! > > The solution is: do not allow stop one policy's governor multi-times > Governor stop should only do once for one policy, after it is stopped, > no other governor stop should be executed. also add one mutext to > protect __cpufreq_governor so governor operation can be kept in sequence. > > Signed-off-by: Xiaoguang Chen <chenxg@xxxxxxxxxxx> > --- > drivers/cpufreq/cpufreq.c | 24 ++++++++++++++++++++++++ > include/linux/cpufreq.h | 1 + > 2 files changed, 25 insertions(+) I forgot to tell you earlier but please update changelog everytime you send a new version. Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
