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Wysocki" , Peter Zijlstra , Frederic Weisbecker , Marcelo Tosatti Subject: [PATCH 02/10] tick/nohz: Conditionally restart tick on idle exit Date: Thu, 13 May 2021 01:29:16 +0200 Message-Id: <20210512232924.150322-3-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210512232924.150322-1-frederic@kernel.org> References: <20210512232924.150322-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yunfeng Ye In nohz_full mode, switching from idle to a task will unconditionally issue a tick restart. If the task is alone in the runqueue or is the highest priority, the tick will fire once then eventually stop. But that alone is still undesired noise. Therefore, only restart the tick on idle exit when it's strictly necessary. Acked-by: Peter Zijlstra Signed-off-by: Yunfeng Ye Cc: Thomas Gleixner Cc: Marcelo Tosatti Cc: Rafael J. Wysocki Signed-off-by: Frederic Weisbecker --- kernel/time/tick-sched.c | 46 +++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 17 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 828b091501ca..05c1ce1034d6 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -926,24 +926,30 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) tick_nohz_restart(ts, now); } -static void tick_nohz_full_update_tick(struct tick_sched *ts) +static void __tick_nohz_full_update_tick(struct tick_sched *ts, + ktime_t now) { #ifdef CONFIG_NO_HZ_FULL int cpu = smp_processor_id(); - if (!tick_nohz_full_cpu(cpu)) - return; - - if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) - return; - if (can_stop_full_tick(cpu, ts)) tick_nohz_stop_sched_tick(ts, cpu); else if (ts->tick_stopped) - tick_nohz_restart_sched_tick(ts, ktime_get()); + tick_nohz_restart_sched_tick(ts, now); #endif } +static void tick_nohz_full_update_tick(struct tick_sched *ts) +{ + if (!tick_nohz_full_cpu(smp_processor_id())) + return; + + if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) + return; + + __tick_nohz_full_update_tick(ts, ktime_get()); +} + static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) { /* @@ -1209,18 +1215,24 @@ static void tick_nohz_account_idle_ticks(struct tick_sched *ts) #endif } -static void __tick_nohz_idle_restart_tick(struct tick_sched *ts, ktime_t now) -{ - tick_nohz_restart_sched_tick(ts, now); - tick_nohz_account_idle_ticks(ts); -} - void tick_nohz_idle_restart_tick(void) { struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); - if (ts->tick_stopped) - __tick_nohz_idle_restart_tick(ts, ktime_get()); + if (ts->tick_stopped) { + tick_nohz_restart_sched_tick(ts, ktime_get()); + tick_nohz_account_idle_ticks(ts); + } +} + +static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now) +{ + if (tick_nohz_full_cpu(smp_processor_id())) + __tick_nohz_full_update_tick(ts, now); + else + tick_nohz_restart_sched_tick(ts, now); + + tick_nohz_account_idle_ticks(ts); } /** @@ -1252,7 +1264,7 @@ void tick_nohz_idle_exit(void) tick_nohz_stop_idle(ts, now); if (tick_stopped) - __tick_nohz_idle_restart_tick(ts, now); + tick_nohz_idle_update_tick(ts, now); local_irq_enable(); } -- 2.25.1