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SubjectRe: [PATCH V2 1/4] cpufreq: stats: Defer stats update to cpufreq_stats_record_transition()
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On 9/16/20 7:45 AM, Viresh Kumar wrote:
> In order to prepare for lock-less stats update, add support to defer any
> updates to it until cpufreq_stats_record_transition() is called.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> drivers/cpufreq/cpufreq_stats.c | 75 ++++++++++++++++++++++++---------
> 1 file changed, 56 insertions(+), 19 deletions(-)
>

[snip]

> @@ -228,10 +264,11 @@ void cpufreq_stats_record_transition(struct cpufreq_policy *policy,
> struct cpufreq_stats *stats = policy->stats;
> int old_index, new_index;
>
> - if (!stats) {
> - pr_debug("%s: No stats found\n", __func__);
> + if (!stats)
> return;
> - }
> +
> + if (READ_ONCE(stats->reset_pending))
> + cpufreq_stats_reset_table(stats);
>

This is in the hot path code, called from the scheduler. I wonder if we
avoid it or make that branch 'unlikely'?

if (unlikely(READ_ONCE(stats->reset_pending)))

Probably the CPU (when it has good prefetcher) would realize about it,
but maybe we can help a bit here.

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