On 19 June 2013 12:30, Xiaoguang Chen <chenxg@xxxxxxxxxxx> wrote: > Cpufreq governor's stop and start operation should be kept in sequence. > If not, there will be unexpected behavior, for example: > > There are 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 (put CPU3 online), > It will call cpufreq_add_policy_cpu in which it first stops userspace > governor, and then starts userspace governor. > > Now if the sequence of above two cases interleaves, It becomes like below: > > 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 policy's governor multi-times. > Governor should only be stopped once for one policy, After it is stopped, > No other governor stop operation should be executed. also add one mutex to > protect __cpufreq_governor so governor operation can be kept in sequence. > > Signed-off-by: Xiaoguang Chen <chenxg@xxxxxxxxxxx> > Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> > --- > drivers/cpufreq/cpufreq.c | 24 ++++++++++++++++++++++++ > include/linux/cpufreq.h | 1 + > 2 files changed, 25 insertions(+) All good now. Sorry for the noise :) -- 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
