From: Frederic Weisbecker <frederic@kernel.org>
To: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
John Stultz <john.stultz@linaro.org>,
Eric Dumazet <edumazet@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
linux-pm@vger.kernel.org, Arjan van de Ven <arjan@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH v3 05/17] timer: Rework idle logic
Date: Wed, 26 Oct 2022 15:27:22 +0200 [thread overview]
Message-ID: <20221026132722.GC1327339@lothringen> (raw)
In-Reply-To: <20221025135850.51044-6-anna-maria@linutronix.de>
On Tue, Oct 25, 2022 at 03:58:38PM +0200, Anna-Maria Behnsen wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> To improve readability of the code, split base->idle calculation and
> expires calculation into separate parts.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
> ---
> kernel/time/timer.c | 29 ++++++++++++++---------------
> 1 file changed, 14 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index f34bc75ff848..cb4194ecca60 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1727,21 +1727,20 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
> base->clk = nextevt;
> }
>
> - if (time_before_eq(nextevt, basej)) {
> - expires = basem;
> - base->is_idle = false;
> - } else {
> - if (base->timers_pending)
> - expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
> - /*
> - * If we expect to sleep more than a tick, mark the base idle.
> - * Also the tick is stopped so any added timer must forward
> - * the base clk itself to keep granularity small. This idle
> - * logic is only maintained for the BASE_STD base, deferrable
> - * timers may still see large granularity skew (by design).
> - */
> - if ((expires - basem) > TICK_NSEC)
> - base->is_idle = true;
> + /*
> + * Base is idle if the next event is more than a tick away. Also
> + * the tick is stopped so any added timer must forward the base clk
> + * itself to keep granularity small. This idle logic is only
> + * maintained for the BASE_STD base, deferrable timers may still
> + * see large granularity skew (by design).
> + */
> + base->is_idle = time_after(nextevt, basej + 1);
A subtle change, yet welcome, is introduced here. If the next event is just
one jiffy ahead, base->is_idle used to be left untouched. So the behaviour
was:
1) If the tick was already stopped (so we must be after an idle IRQ),
base->is_idle remains true
2) If the tick was not yet stopped, base->is_idle remains false
After this patch, 1) becomes:
1) If the tick was already stopped, turn base->is_idle to false
As a result, we may spare an IPI if we remotely enqueue a timer to
an idle CPU that is going to tick on the next jiffy.
Whether it's worth mentioning in the changelog, I leave it to you.
> +
> + if (base->timers_pending) {
> + /* If we missed a tick already, force 0 delta */
> + if (time_before_eq(nextevt, basej))
> + nextevt = basej;
Can be time_before() then, right?
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
> + expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
> }
> raw_spin_unlock(&base->lock);
>
> --
> 2.30.2
>
next prev parent reply other threads:[~2022-10-26 13:27 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-25 13:58 [PATCH v3 00/17] timer: Move from a push remote at enqueue to a pull at expiry model Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 01/17] cpufreq: Prepare timer flags for hierarchical timer pull model Anna-Maria Behnsen
2022-10-26 13:54 ` Frederic Weisbecker
2022-10-31 15:22 ` Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 02/17] tick-sched: Warn when next tick seems to be in the past Anna-Maria Behnsen
2022-10-25 22:11 ` Frederic Weisbecker
2022-10-25 13:58 ` [PATCH v3 03/17] timer: Move store of next event into __next_timer_interrupt() Anna-Maria Behnsen
2022-10-26 9:33 ` Frederic Weisbecker
2022-10-25 13:58 ` [PATCH v3 04/17] timer: Split next timer interrupt logic Anna-Maria Behnsen
2022-10-26 9:40 ` Frederic Weisbecker
2022-10-25 13:58 ` [PATCH v3 05/17] timer: Rework idle logic Anna-Maria Behnsen
2022-10-26 13:27 ` Frederic Weisbecker [this message]
2022-10-25 13:58 ` [PATCH v3 06/17] timer: Keep the pinned timers separate from the others Anna-Maria Behnsen
2022-10-26 15:26 ` Frederic Weisbecker
2022-10-25 13:58 ` [PATCH v3 07/17] timer: Retrieve next expiry of pinned/non-pinned timers seperately Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 08/17] timer: Rename get_next_timer_interrupt() Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 09/17] timer: Split out "get next timer interrupt" functionality Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 10/17] timer: Add get next timer interrupt functionality for remote CPUs Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 11/17] timer: Restructure internal locking Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 12/17] timer: Check if timers base is handled already Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 13/17] tick/sched: Split out jiffies update helper function Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 14/17] timer: Implement the hierarchical pull model Anna-Maria Behnsen
2022-10-25 16:36 ` kernel test robot
2022-10-26 5:35 ` kernel test robot
2022-10-27 7:38 ` kernel test robot
2022-10-25 13:58 ` [PATCH v3 15/17] timer_migration: Add tracepoints Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 16/17] add_timer_on(): Make sure callers have TIMER_PINNED flag Anna-Maria Behnsen
2022-10-25 13:58 ` [PATCH v3 17/17] timer: Always queue timers on the local CPU Anna-Maria Behnsen
2022-10-27 7:22 ` kernel test robot
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