On Thu, Feb 8, 2018 at 6:01 PM, Claudio Scordino
<clau...@evidence.eu.com> wrote:
> When the SCHED_DEADLINE scheduling class increases the CPU utilization,
> we should not wait for the rate limit, otherwise we may miss some deadline.
>
> Tests using rt-app on Exynos5422 have shown reductions of about 10% of
> deadline
> misses for tasks with low RT periods.
>
> The patch applies on top of the one recently proposed by Peter to drop the
> SCHED_CPUFREQ_* flags.
>
> Signed-off-by: Claudio Scordino <clau...@evidence.eu.com>
> CC: Rafael J . Wysocki <rafael.j.wyso...@intel.com>
> CC: Patrick Bellasi <patrick.bell...@arm.com>
> CC: Dietmar Eggemann <dietmar.eggem...@arm.com>
> CC: Morten Rasmussen <morten.rasmus...@arm.com>
> CC: Juri Lelli <juri.le...@redhat.com>
> CC: Viresh Kumar <viresh.ku...@linaro.org>
> CC: Vincent Guittot <vincent.guit...@linaro.org>
> CC: Todd Kjos <tk...@android.com>
> CC: Joel Fernandes <joe...@google.com>
> CC: linux...@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> ---
> kernel/sched/cpufreq_schedutil.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c
> b/kernel/sched/cpufreq_schedutil.c
> index b0bd77d..d8dcba2 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -74,7 +74,10 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);
>
> /************************ Governor internals ***********************/
>
> -static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64
> time)
> +static bool sugov_should_update_freq(struct sugov_policy *sg_policy,
> + u64 time,
> + struct sugov_cpu *sg_cpu_old,
> + struct sugov_cpu *sg_cpu_new)
This looks somewhat excessive for using just one field from each of these.
> {
> s64 delta_ns;
>
> @@ -111,6 +114,10 @@ static bool sugov_should_update_freq(struct sugov_policy
> *sg_policy, u64 time)
> return true;
> }
>
> + /* Ignore rate limit when DL increased utilization. */
> + if (sg_cpu_new->util_dl > sg_cpu_old->util_dl)
> + return true;
> +
> delta_ns = time - sg_policy->last_freq_update_time;
> return delta_ns >= sg_policy->freq_update_delay_ns;
> }
> @@ -271,6 +278,7 @@ static void sugov_update_single(struct update_util_data
> *hook, u64 time,
> unsigned int flags)
> {
> struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu,
> update_util);
> + struct sugov_cpu sg_cpu_old = *sg_cpu;
And here you copy the entire struct to pass a pointer to the copy to a
helper function so that it can access one field.
That doesn't look particularly straightforward to me, let alone the overhead.
I guess you may do the check before calling sugov_should_update_freq()
and set sg_policy->need_freq_update if its true, as you know upfront
that the previous sg_policy->next_freq value isn't going to be used
anyway in that case.
