Hi, Rafael When can this patch be merged? 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 > -- 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
