2013/6/10 Viresh Kumar <viresh.kumar@xxxxxxxxxx>:
> On 9 June 2013 13:20, 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 governor multi-times
>> Governor stop should only do once, after it is stopped,
>> no other governor stop should be executed.
>>
>> Signed-off-by: Xiaoguang Chen <chenxg@xxxxxxxxxxx>
>> ---
>> drivers/cpufreq/cpufreq.c | 10 +++++++++-
>> include/linux/cpufreq.h | 1 +
>> 2 files changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 2d53f47..c8d7cb2 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -1562,6 +1562,11 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
>>
>> pr_debug("__cpufreq_governor for CPU %u, event %u\n",
>> policy->cpu, event);
>> +
>> + if ((!policy->governor->enabled && (event == CPUFREQ_GOV_STOP)) ||
>> + (policy->governor->enabled && (event == CPUFREQ_GOV_START)))
>> + return 0;
>> +
>> ret = policy->governor->governor(policy, event);
>>
>> if (!ret) {
>> @@ -1569,6 +1574,10 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
>> policy->governor->initialized++;
>> else if (event == CPUFREQ_GOV_POLICY_EXIT)
>> policy->governor->initialized--;
>> + else if (event == CPUFREQ_GOV_STOP)
>> + policy->governor->enabled = 0;
>> + else if (event == CPUFREQ_GOV_START)
>> + policy->governor->enabled = 1;
>> }
>>
>> /* we keep one module reference alive for
>> @@ -1581,7 +1590,6 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
>> return ret;
>> }
>>
>> -
>> int cpufreq_register_governor(struct cpufreq_governor *governor)
>> {
>> int err;
>> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
>> index 037d36a..16c5b70 100644
>> --- a/include/linux/cpufreq.h
>> +++ b/include/linux/cpufreq.h
>> @@ -199,6 +199,7 @@ struct cpufreq_governor {
>> will fallback to performance governor */
>> struct list_head governor_list;
>> struct module *owner;
>> + int enabled;
>> };
>
> This isn't sufficient.
>
> If there are two groups of clk-sharing-cpus, i.e. if we have multiple
> policies and they are using same governor, then these functions
> gets called twice for governor x. And you will return 0 for the second
> policy.
So this enable flag should be per policy, right?
I'll modify this patch
Thanks
Xiaoguang
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