On 03/13/2014 11:06 PM, dirk.brande...@gmail.com wrote:
> From: Dirk Brandewie <dirk.j.brande...@intel.com>
>
> This callback allows the driver to do clean up before the CPU is
> completely down and its state cannot be modified. This is used
> by the intel_pstate driver to reduce the requested P state prior to
> the core going away. This is required because the requested P state
> of the offline core is used to select the package P state. This
> effectively sets the floor package P state to the requested P state on
> the offline core.
>
> Signed-off-by: Dirk Brandewie <dirk.j.brande...@intel.com>
> ---
> Documentation/cpu-freq/cpu-drivers.txt | 8 +++++++-
> drivers/cpufreq/cpufreq.c | 3 +++
> include/linux/cpufreq.h | 1 +
> 3 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/cpu-freq/cpu-drivers.txt
> b/Documentation/cpu-freq/cpu-drivers.txt
> index 8b1a445..935f274 100644
> --- a/Documentation/cpu-freq/cpu-drivers.txt
> +++ b/Documentation/cpu-freq/cpu-drivers.txt
> @@ -61,7 +61,13 @@ target_index - See below on the
> differences.
>
> And optionally
>
> -cpufreq_driver.exit - A pointer to a per-CPU cleanup function.
> +cpufreq_driver.exit - A pointer to a per-CPU cleanup
> + function called during CPU_POST_DEAD
> + phase of cpu hotplug process.
> +
> +cpufreq_driver.exit_prepare - A pointer to a per-CPU cleanup function
> + called during CPU_DOWN_PREPARE phase of
> + cpu hotplug process.
>
> cpufreq_driver.resume - A pointer to a per-CPU resume function
> which is called with interrupts disabled
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index cf485d9..5c9bbfa 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1338,6 +1338,9 @@ static int __cpufreq_remove_dev_prepare(struct device
> *dev,
> }
> }
>
> + if (cpufreq_driver->exit_prepare)
> + cpufreq_driver->exit_prepare(policy);
> +
The placement of this hunk doesn't feel right. IMHO we should place it
right next to the code which stops the governor.
Something like this:
if (has_target()) {
ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
if (ret) {
pr_err("%s: Failed to stop governor\n", __func__);
return ret;
}
} else if (cpufreq_driver->setpolicy) {
if (cpufreq_driver->exit_prepare)
cpufreq_driver->exit_prepare(policy);
}
This makes it clear that GOV_STOP is used to stop managing the CPUs
for platforms that have ->target defined, and ->exit_prepare() is used
for similar purposes for platforms that have ->setpolicy() defined.
By the way, I like the name ->stop more than ->exit_prepare, because:
->exit() is done once per policy, which implies that ->exit_prepare
also shares similar semantics. However, what we really want the new
callback to do is to provide a way for the driver to stop managing the
CPU that is going offline, just like GOV_STOP. So naturally, this
new callback should be invoked during every CPU offline, and not just
once per policy. Hence the name "stop" (this CPU) makes perfect sense
for that IMHO.
[Of course, I understand that GOV_STOP actually stops the entire
policy for all affected cpus and then we use GOV_START in
_remove_dev_finish() to restart the governor for the other online
CPUs in that policy. This is somewhat round-about, but conceptually
this is equivalent to asking the governor to let go control of only
the CPU going offline. The new ->stop callback should have the same
"stop only this CPU" semantics.]
> return 0;
> }
>
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 4d89e0e..5fa94ad 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -224,6 +224,7 @@ struct cpufreq_driver {
> int (*bios_limit) (int cpu, unsigned int *limit);
>
> int (*exit) (struct cpufreq_policy *policy);
> + int (*exit_prepare) (struct cpufreq_policy *policy);
> int (*suspend) (struct cpufreq_policy *policy);
> int (*resume) (struct cpufreq_policy *policy);
> struct freq_attr **attr;
>
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