Messages in this thread | | | Date | Wed, 18 May 2016 23:22:16 +0200 | Subject | Re: [RFC PATCH] cpufreq: powernv: Add fast_switch callback | From | "Rafael J. Wysocki" <> |
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On Wed, May 18, 2016 at 2:53 PM, Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> wrote: > Add fast_switch driver callback to support frequency update in > interrupt context while using schedutil governor. Changing frequency > in interrupt context will remove the jitter on the workloads which can > be seen when a kworker thread is used for the changing the frequency. > > Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
This looks simple enough. :-)
A couple of comments, though.
> --- > drivers/cpufreq/powernv-cpufreq.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c > index 54c4536..4553eb6 100644 > --- a/drivers/cpufreq/powernv-cpufreq.c > +++ b/drivers/cpufreq/powernv-cpufreq.c > @@ -678,6 +678,8 @@ static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy) > for (i = 0; i < threads_per_core; i++) > cpumask_set_cpu(base + i, policy->cpus); > > + policy->fast_switch_possible = true; > + > kn = kernfs_find_and_get(policy->kobj.sd, throttle_attr_grp.name); > if (!kn) { > int ret; > @@ -854,6 +856,24 @@ static void powernv_cpufreq_stop_cpu(struct cpufreq_policy *policy) > del_timer_sync(&gpstates->timer); > } > > +static unsigned int powernv_fast_switch(struct cpufreq_policy *policy, > + unsigned int target_freq) > +{ > + int index; > + struct powernv_smp_call_data freq_data; > + > + cpufreq_frequency_table_target(policy, policy->freq_table, > + target_freq, > + CPUFREQ_RELATION_C, &index);
According to the discussion I had with Peter some time ago, this should be RELATION_L or you may end up using a frequency that's not sufficient to meet a deadline somewhere.
Also cpufreq_frequency_table_target() is somewhat heavy-weight especially if the table is known to be sorted (which I guess is the case).
> + if (index < 0 || index >= powernv_pstate_info.nr_pstates) > + return CPUFREQ_ENTRY_INVALID; > + freq_data.pstate_id = powernv_freqs[index].driver_data; > + freq_data.gpstate_id = powernv_freqs[index].driver_data; > + set_pstate(&freq_data); > + > + return pstate_id_to_freq(-index); > +} > + > static struct cpufreq_driver powernv_cpufreq_driver = { > .name = "powernv-cpufreq", > .flags = CPUFREQ_CONST_LOOPS, > @@ -861,6 +881,7 @@ static struct cpufreq_driver powernv_cpufreq_driver = { > .exit = powernv_cpufreq_cpu_exit, > .verify = cpufreq_generic_frequency_table_verify, > .target_index = powernv_cpufreq_target_index, > + .fast_switch = powernv_fast_switch, > .get = powernv_cpufreq_get, > .stop_cpu = powernv_cpufreq_stop_cpu, > .attr = powernv_cpu_freq_attr, > --
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