Messages in this thread Patch in this message |  | | Subject | Re: nohz: Update tick instead of restarting tick in tick_nohz_idle_exit() | From | Yunfeng Ye <> | Date | Fri, 19 Feb 2021 21:08:47 +0800 |
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On 2021/2/19 20:16, Frederic Weisbecker wrote: > On Mon, Nov 23, 2020 at 09:22:08PM +0800, Yunfeng Ye wrote: >> In realtime scenarios, the "nohz_full" parameter is configured. Tick >> interference is not expected when there is only one realtime thread. >> But when the idle thread is switched to the realtime thread, the tick >> timer is restarted always. >> >> So on the nohz full mode, it is unnecessary to restart the tick timer >> when there is only one realtime thread. Adding can_stop_full_tick() >> before restarting the tick, if it return true, keep tick stopped. >> >> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> > > Hi, > > After reworking the codebase a bit, I've edited your patch and > changelog and then queued it. I'll post it in a series after the > merge window. See the result: > Ok, Thanks. My first version patch which not be sent is a little like this.
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index cc7cba20382e..e793c8f675e6 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -908,21 +908,24 @@ 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 int 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; + return -EINVAL;
if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) - return; + return -EINVAL;
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); + return 0; +#else + return -EINVAL; #endif }
@@ -1080,7 +1083,7 @@ void tick_nohz_irq_exit(void) if (ts->inidle) tick_nohz_start_idle(ts); else - tick_nohz_full_update_tick(ts); + tick_nohz_full_update_tick(ts, ktime_get()); }
/** @@ -1208,6 +1211,13 @@ void tick_nohz_idle_restart_tick(void) __tick_nohz_idle_restart_tick(ts, ktime_get()); }
+static void tick_nohz_update_tick(struct tick_sched *ts, ktime_t now) +{ + if (tick_nohz_full_update_tick(ts) < 0) + tick_nohz_restart_sched_tick(ts, now); + tick_nohz_account_idle_ticks(ts); +} + /** * tick_nohz_idle_exit - restart the idle tick from the idle task * @@ -1237,7 +1247,7 @@ void tick_nohz_idle_exit(void) tick_nohz_stop_idle(ts, now);
if (tick_stopped) - __tick_nohz_idle_restart_tick(ts, now); + tick_nohz_update_tick(ts, now);
local_irq_enable(); }
> --- > From: Yunfeng Ye <yeyunfeng@huawei.com> > Date: Tue, 9 Feb 2021 23:59:19 +0100 > Subject: [PATCH] tick/nohz: Conditionally restart tick on idle exit > > 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. > > Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > --- > kernel/time/tick-sched.c | 44 ++++++++++++++++++++++++---------------- > 1 file changed, 27 insertions(+), 17 deletions(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 3e272490fe2e..79796286a4ba 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -923,24 +923,28 @@ 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; > + int cpu = smp_processor_id(); > > + 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, now); > +#endif > +} > + > +static void tick_nohz_full_update_tick(struct tick_sched *ts) > +{ > if (!tick_nohz_full_this_cpu()) > return; > > if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) > return; > > - cpu = smp_processor_id(); > - > - 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()); > -#endif > + __tick_nohz_full_update_tick(ts, ktime_get()); > } > > static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) > @@ -1210,18 +1214,24 @@ 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) > +void tick_nohz_idle_restart_tick(void) > { > - tick_nohz_restart_sched_tick(ts, now); > - tick_nohz_account_idle_ticks(ts); > + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); > + > + if (ts->tick_stopped) { > + tick_nohz_restart_sched_tick(ts, ktime_get()); > + tick_nohz_account_idle_ticks(ts); > + } > } > > -void tick_nohz_idle_restart_tick(void) > +static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now) > { > - struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); > + if (tick_nohz_full_this_cpu()) > + __tick_nohz_full_update_tick(ts, now); > + else > + tick_nohz_restart_sched_tick(ts, now); > > - if (ts->tick_stopped) > - __tick_nohz_idle_restart_tick(ts, ktime_get()); > + tick_nohz_account_idle_ticks(ts); > } > > /** > @@ -1253,7 +1263,7 @@ 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(); > } >
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