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Wysocki" Cc: Christian Loehle , Thomas Gleixner , LKML , Peter Zijlstra , Frederic Weisbecker , Linux PM Subject: Re: [patch 2/2] sched/idle: Make default_idle_call() NOHZ aware Message-ID: <20260310035406.xnu3nlqp4ldshxww@airbuntu> References: <20260301191959.406218221@kernel.org> <6250711.lOV4Wx5bFT@rafael.j.wysocki> <2409653.ElGaqSPkdT@rafael.j.wysocki> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <2409653.ElGaqSPkdT@rafael.j.wysocki> On 03/07/26 17:25, Rafael J. Wysocki wrote: > In the meantime I realized that if the .select() governor > callback is skipped, its .reflect() callback should be skipped > either, so I've posted this: > > https://lkml.org/lkml/2026/3/7/569 > > and here's a fixed version of the last patch on top of the above (for > completeness): > > --- > kernel/sched/idle.c | 25 ++++++++++++++++--------- > 1 file changed, 16 insertions(+), 9 deletions(-) > > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -161,6 +161,14 @@ static int call_cpuidle(struct cpuidle_d > return cpuidle_enter(drv, dev, next_state); > } > > +static void idle_call_stop_or_retain_tick(bool stop_tick) > +{ > + if (stop_tick || tick_nohz_tick_stopped()) > + tick_nohz_idle_stop_tick(); > + else > + tick_nohz_idle_retain_tick(); > +} > + > /** > * cpuidle_idle_call - the main idle function > * > @@ -170,7 +178,7 @@ static int call_cpuidle(struct cpuidle_d > * set, and it returns with polling set. If it ever stops polling, it > * must clear the polling bit. > */ > -static void cpuidle_idle_call(void) > +static void cpuidle_idle_call(bool stop_tick) > { > struct cpuidle_device *dev = cpuidle_get_device(); > struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev); > @@ -186,7 +194,7 @@ static void cpuidle_idle_call(void) > } > > if (cpuidle_not_available(drv, dev)) { > - tick_nohz_idle_stop_tick(); > + idle_call_stop_or_retain_tick(stop_tick); > > default_idle_call(); > goto exit_idle; > @@ -222,17 +230,14 @@ static void cpuidle_idle_call(void) > next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns); > call_cpuidle(drv, dev, next_state); > } else if (drv->state_count > 1) { > - bool stop_tick = true; > + stop_tick = true; Silly question, but wouldn't this benefit the normal path too to delay for one tick? This will only matter for the cases where the governor doesn't explicitly set stop_tick to either true or false - which I am not sure what they are :) > > /* > * Ask the cpuidle framework to choose a convenient idle state. > */ > next_state = cpuidle_select(drv, dev, &stop_tick); > > - if (stop_tick || tick_nohz_tick_stopped()) > - tick_nohz_idle_stop_tick(); > - else > - tick_nohz_idle_retain_tick(); > + idle_call_stop_or_retain_tick(stop_tick); > > entered_state = call_cpuidle(drv, dev, next_state); > /* > @@ -240,7 +245,7 @@ static void cpuidle_idle_call(void) > */ > cpuidle_reflect(dev, entered_state); > } else { > - tick_nohz_idle_retain_tick(); > + idle_call_stop_or_retain_tick(stop_tick); > > /* > * If there is only a single idle state (or none), there is > @@ -268,6 +273,7 @@ exit_idle: > static void do_idle(void) > { > int cpu = smp_processor_id(); > + bool got_tick = false; > > /* > * Check if we need to update blocked load > @@ -338,8 +344,9 @@ static void do_idle(void) > tick_nohz_idle_restart_tick(); > cpu_idle_poll(); > } else { > - cpuidle_idle_call(); > + cpuidle_idle_call(got_tick); > } > + got_tick = tick_nohz_idle_got_tick(); > arch_cpu_idle_exit(); > } > > > >