Messages in this thread | | | Date | Thu, 21 Feb 2013 11:49:03 -0600 | From | Nathan Zimmer <> | Subject | Re: [PATCH v3 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu |
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On 02/20/2013 11:50 PM, Viresh Kumar wrote: > On 21 February 2013 05:26, Nathan Zimmer <nzimmer@sgi.com> 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@linaro.org> >> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> >> Signed-off-by: Nathan Zimmer <nzimmer@sgi.com> >> --- >> 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. Of course. >> 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. Good point. I placed a similar sycnronize_rcu in cpufreq_add_policy_cpu and cpufreq_add_dev. I will remove them also.
Thanks, I will respin. Nate
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