On Mon, May 9, 2016 at 11:20 PM, Steve Muckle <steve.muc...@linaro.org> wrote:
> The mechanisms for remote CPU updates and slow-path frequency
> transitions are relatively expensive - the former is an IPI while the
> latter requires waking up a thread to do work. These activities should
> be avoided if they are not necessary. To that end, calculate the
> actual target-supported frequency required by the new utilization
> value in schedutil. If it is the same as the previously requested
> frequency then there is no need to continue with the update.
Unless the max/min limits changed in the meantime, right?
>
> Signed-off-by: Steve Muckle <smuc...@linaro.org>
> ---
> kernel/sched/cpufreq_schedutil.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c
> b/kernel/sched/cpufreq_schedutil.c
> index 6cb2ecc204ec..e185075fcb5c 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -153,14 +153,26 @@ static void sugov_update_commit(struct sugov_cpu
> *sg_cpu, int cpu, u64 time,
> * next_freq = C * curr_freq * util_raw / max
> *
> * Take C = 1.25 for the frequency tipping point at (util / max) = 0.8.
> + *
> + * The lowest target-supported frequency which is equal or greater than the
> raw
> + * next_freq (as calculated above) is returned, or the CPU's max_freq if such
> + * a target-supported frequency does not exist.
> */
> static unsigned int get_next_freq(struct cpufreq_policy *policy,
> unsigned long util, unsigned long max)
> {
> + struct cpufreq_frequency_table *entry;
> unsigned int freq = arch_scale_freq_invariant() ?
> policy->cpuinfo.max_freq : policy->cur;
> + unsigned int target_freq = UINT_MAX;
> +
> + freq = (freq + (freq >> 2)) * util / max;
> +
> + cpufreq_for_each_valid_entry(entry, policy->freq_table)
> + if (entry->frequency >= freq && entry->frequency <
> target_freq)
> + target_freq = entry->frequency;
Please don't assume that every driver will have a frequency table.
That may not be the case in the future (and I'm not even sure about
the existing CPPC driver for that matter).
>
> - return (freq + (freq >> 2)) * util / max;
> + return target_freq != UINT_MAX ? target_freq :
> policy->cpuinfo.max_freq;
> }
>
> static void sugov_update_single(struct update_util_data *hook, u64 time,
> --
> 2.4.10
>
