lkml.org 
[lkml]   [2009]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [patch 2/3] cpufreq: Define dbs_mutex purpose and cleanup its usage
    From
    Date
    On Thu, 2009-06-25 at 12:46 -0700, Mathieu Desnoyers wrote:
    > * venkatesh.pallipadi@intel.com (venkatesh.pallipadi@intel.com) wrote:
    > > Commit b14893a62c73af0eca414cfed505b8c09efc613c although it was very
    > > much needed to cleanup ondemand timer cleanly, openup a can of worms
    > > related to locking dependencies in cpufreq.
    > >
    > > Patch here defines the need for dbs_mutex and cleans up its usage in
    > > ondemand governor. This also resolves the lockdep warnings reported here
    > >
    > > http://lkml.indiana.edu/hypermail/linux/kernel/0906.1/01925.html
    > >

    > > @@ -598,14 +593,16 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
    > > max(min_sampling_rate,
    > > latency * LATENCY_MULTIPLIER);
    > > }
    > > + mutex_unlock(&dbs_mutex);
    > > +
    > > dbs_timer_init(this_dbs_info);
    > >
    > > - mutex_unlock(&dbs_mutex);
    > > break;
    > >
    > > case CPUFREQ_GOV_STOP:
    > > - mutex_lock(&dbs_mutex);
    > > dbs_timer_exit(this_dbs_info);
    >
    > Hrm, so.. how do we protect against concurrent :
    >
    > CPUFREQ_GOV_START/CPUFREQ_GOV_STOP now ?

    concurrent _START _STOP across CPUs does not matter for timer_init and
    timer_exit. On same CPU, there cannot be two concurrent _START as upper
    level cpufreq will have policy_rwsem in write mode. I cannot think of a
    flow where _START and _STOP on same CPU is possible.

    However two concurrent _STOP for same CPU is still possible, as we are
    releasing the rwsem lock before STOP callback. "Back to drawing board"
    time to figure this all out..

    Thanks,
    Venki



    \
     
     \ /
      Last update: 2009-06-25 22:59    [W:0.038 / U:121.524 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site