From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Byungchul Park <byungchul.park@lge.com>,
Chris Metcalf <cmetcalf@ezchip.com>,
Thomas Gleixner <tglx@linutronix.de>,
Luiz Capitulino <lcapitulino@redhat.com>,
Christoph Lameter <cl@linux.com>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting
Date: Fri, 8 Apr 2016 11:41:54 +0200 [thread overview]
Message-ID: <20160408094153.GL3448@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1460077633-23431-3-git-send-email-fweisbec@gmail.com>
On Fri, Apr 08, 2016 at 03:07:12AM +0200, Frederic Weisbecker wrote:
> +void cpu_load_update_nohz_start(void)
> {
> struct rq *this_rq = this_rq();
> +
> + /*
> + * This is all lockless but should be fine. If weighted_cpuload changes
> + * concurrently we'll exit nohz. And cpu_load write can race with
> + * cpu_load_update_idle() but both updater would be writing the same.
> + */
> + this_rq->cpu_load[0] = weighted_cpuload(cpu_of(this_rq));
> +}
There is more to this; this also updates ->cpu_load[0] at possibly much
higher frequency than we've done before, while not updating the other
->cpu_load[] members.
Now, I'm not sure we care, but it is a bit odd.
> +/*
> + * Account the tickless load in the end of a nohz frame.
> + */
> +void cpu_load_update_nohz_stop(void)
> +{
> unsigned long curr_jiffies = READ_ONCE(jiffies);
> + struct rq *this_rq = this_rq();
> + unsigned long load;
>
> if (curr_jiffies == this_rq->last_load_update_tick)
> return;
>
> + load = weighted_cpuload(cpu_of(this_rq));
> raw_spin_lock(&this_rq->lock);
> + cpu_load_update_nohz(this_rq, curr_jiffies, load);
> raw_spin_unlock(&this_rq->lock);
> }
And this makes us take rq->lock when waking from nohz; a bit
unfortunate. Do we really need this though? Will not a tick be
forthcoming real-soon-now?
next prev parent reply other threads:[~2016-04-08 9:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-08 1:07 [PATCH 0/3] sched: Fix/improve nohz cpu load updates v2 Frederic Weisbecker
2016-04-08 1:07 ` [PATCH 1/3] sched: Gather cpu load functions under a more conventional namespace Frederic Weisbecker
2016-04-08 1:07 ` [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting Frederic Weisbecker
2016-04-08 9:41 ` Peter Zijlstra [this message]
2016-04-08 12:53 ` Frederic Weisbecker
2016-04-08 17:40 ` Peter Zijlstra
2016-04-08 1:07 ` [PATCH 3/3] sched: Optimize !CONFIG_NO_HZ_COMMON cpu load updates Frederic Weisbecker
2016-04-08 10:48 ` Peter Zijlstra
2016-04-08 12:55 ` Frederic Weisbecker
2016-04-08 17:44 ` Peter Zijlstra
2016-04-11 13:18 ` Frederic Weisbecker
2016-04-11 14:53 ` Chris Metcalf
2016-04-11 18:21 ` Frederic Weisbecker
2016-04-12 14:23 ` Peter Zijlstra
2016-04-13 13:56 [PATCH 0/3] sched: Fix/improve nohz cpu load updates v3 Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting Frederic Weisbecker
2016-04-18 8:22 ` Byungchul Park
2016-04-18 9:17 ` Byungchul Park
2016-04-18 13:35 ` Frederic Weisbecker
2016-04-19 0:01 ` Byungchul Park
2016-04-19 14:01 ` Frederic Weisbecker
2016-04-20 7:59 ` Wanpeng Li
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