From: Peter Zijlstra <peterz@infradead.org>
To: shrikanth hegde <sshegde@linux.vnet.ibm.com>
Cc: mingo@redhat.com, Vincent Guittot <vincent.guittot@linaro.org>,
dietmar.eggemann@arm.com, bsegall@google.com,
Thomas Gleixner <tglx@linutronix.de>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Arjan van de Ven <arjan@linux.intel.com>,
svaidy@linux.ibm.com, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] sched/fair: Interleave cfs bandwidth timers for improved single thread performance at low utilization
Date: Mon, 20 Feb 2023 18:38:00 +0100 [thread overview]
Message-ID: <Y/Ov+DzOtA0iHfFO@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <9c57c92c-3e0c-b8c5-4be9-8f4df344a347@linux.vnet.ibm.com>
On Tue, Feb 14, 2023 at 08:54:09PM +0530, shrikanth hegde wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ff4dbbae3b10..7b69c329e05d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5939,14 +5939,25 @@ static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
>
> void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> {
> - lockdep_assert_held(&cfs_b->lock);
> + struct hrtimer *period_timer = &cfs_b->period_timer;
> + s64 incr = ktime_to_ns(cfs_b->period) / 10;
> + ktime_t delta;
> + u64 orun = 1;
>
> + lockdep_assert_held(&cfs_b->lock);
> if (cfs_b->period_active)
> return;
>
> cfs_b->period_active = 1;
> - hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
> - hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
> + delta = ktime_sub(period_timer->base->get_time(),
> + hrtimer_get_expires(period_timer));
> + if (unlikely(delta >= cfs_b->period)) {
> + orun = ktime_divns(delta, incr);
> + hrtimer_add_expires_ns(period_timer, incr * orun);
> + }
> +
> + hrtimer_forward_now(period_timer, cfs_b->period);
> + hrtimer_start_expires(period_timer, HRTIMER_MODE_ABS_PINNED);
> }
What kind of mad hackery is this? Why can't you do the sane thing and
initialize the timer at !0 in init_cfs_bandwidth(), then any of the
forwards will stay in period -- as they should.
Please, go re-read Thomas's email.
*completely* untested...
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c46485d65d7..4d6ea76096dc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5915,6 +5915,7 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
+ cfs_b->period_timer.node.expires = get_random_u32_below(cfs_b->period);
cfs_b->period_timer.function = sched_cfs_period_timer;
hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
cfs_b->slack_timer.function = sched_cfs_slack_timer;
next prev parent reply other threads:[~2023-02-20 17:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-14 15:24 [RFC PATCH] sched/fair: Interleave cfs bandwidth timers for improved single thread performance at low utilization shrikanth hegde
2023-02-20 17:38 ` Peter Zijlstra [this message]
2023-02-21 18:53 ` shrikanth hegde
2023-02-21 21:43 ` Benjamin Segall
2023-02-22 9:36 ` Peter Zijlstra
[not found] <20230214120502.934324-1-sshegde@linux.vnet.ibm.com>
2023-02-14 21:37 ` Benjamin Segall
2023-02-15 11:01 ` shrikanth hegde
2023-02-15 21:32 ` Benjamin Segall
2023-02-16 19:57 ` shrikanth hegde
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