On Monday, June 24, 2013 02:04:50 PM Xiaoguang Chen wrote: > Hi, Rafael > When can this patch be merged? Well, it's in my bleeding-edge branch. If it doesn't break builds, it will go to linux-next for 3.11. Thanks, Rafael > 2013/6/19 Xiaoguang Chen <chenxg@xxxxxxxxxxx>: > > On 06/19/2013 03:55 PM, Viresh Kumar wrote: > >> > >> 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 :) > > > > Thank you for the professional instructions. It makes the code more > > beautiful. :) > > > > -- > > Thanks > > Xiaoguang > > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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
