On 21 February 2013 05:26, Nathan Zimmer <nzimmer@xxxxxxx> wrote:
> In general rwlocks are discourged so we are moving it to use the rcu instead.
> This does require a bit of care since the cpufreq_driver_lock protects both
> the cpufreq_driver and the cpufreq_cpu_data array.
> Also since many of the function pointers on cpufreq_driver may sleep when
> called we have to grab them under the rcu_read_lock but call them after
> rcu_read_unlock();
Even i have started reading rcu documentation now :)
> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
> Signed-off-by: Nathan Zimmer <nzimmer@xxxxxxx>
> ---
> drivers/cpufreq/cpufreq.c | 312 +++++++++++++++++++++++++++++++++-------------
> 1 file changed, 224 insertions(+), 88 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> @@ -255,20 +258,21 @@ static inline void adjust_jiffies(unsigned long val, struct cpufreq_freqs *ci)
> void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
> {
> struct cpufreq_policy *policy;
> - unsigned long flags;
> + u8 flags;
I think you can get rid of flags.
> BUG_ON(irqs_disabled());
>
> if (cpufreq_disabled())
> return;
>
> - freqs->flags = cpufreq_driver->flags;
> pr_debug("notification %u of frequency transition to %u kHz\n",
> state, freqs->new);
>
> - read_lock_irqsave(&cpufreq_driver_lock, flags);
> + rcu_read_lock();
> + flags = rcu_dereference(cpufreq_driver)->flags;
use freq->flags here ...
> policy = per_cpu(cpufreq_cpu_data, freqs->cpu);
> - read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> + rcu_read_unlock();
> + freqs->flags = flags;
>
> switch (state) {
>
> @@ -277,7 +281,7 @@ void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
> * which is not equal to what the cpufreq core thinks is
> * "old frequency".
> */
> - if (!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
> + if (!(flags & CPUFREQ_CONST_LOOPS)) {
and here.
> if ((policy) && (policy->cpu == freqs->cpu) &&
> (policy->cur) && (policy->cur != freqs->old)) {
> pr_debug("Warning: CPU frequency is"
> @@ -742,35 +773,39 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
> - write_lock_irqsave(&cpufreq_driver_lock, flags);
> + spin_lock_irqsave(&cpufreq_driver_lock, flags);
> for_each_cpu(j, policy->cpus) {
> per_cpu(cpufreq_cpu_data, j) = policy;
> per_cpu(cpufreq_policy_cpu, j) = policy->cpu;
> }
> - write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> + spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
> + synchronize_rcu();
I don't think (but i can be wrong too :) ), that we need a synchronize_rcu()
here. We need it only at places where we have updated the cpufreq_driver
pointer.
As we aren't doing any rcu specific read/update for cpufreq_cpu_data.
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