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Wysocki" , Thomas Gleixner , LKML , Peter Zijlstra , Frederic Weisbecker , Linux PM Subject: Re: [patch 2/2] sched/idle: Make default_idle_call() NOHZ aware Message-ID: <20260310150347.ji2fdpdvw6txspc4@airbuntu> References: <20260301191959.406218221@kernel.org> <6250711.lOV4Wx5bFT@rafael.j.wysocki> <2409653.ElGaqSPkdT@rafael.j.wysocki> <20260310035406.xnu3nlqp4ldshxww@airbuntu> Precedence: bulk X-Mailing-List: linux-kernel@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: On 03/10/26 09:18, Christian Loehle wrote: > On 3/10/26 03:54, Qais Yousef wrote: > > 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 :) > > > Right now the governors will always set stop_tick explicitly (and overriding > that might confuse the governor-internal state). So we can drop this hunk then