From: Peter Zijlstra <peterz@infradead.org>
To: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>,
tglx@linutronix.de, rafael@kernel.org, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org, vincent.guittot@linaro.org
Subject: Re: [RFC V2 2/2] sched: idle: IRQ based next prediction for idle period
Date: Wed, 20 Jan 2016 20:29:52 +0100 [thread overview]
Message-ID: <20160120192952.GU6357@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.LFD.2.20.1601201408430.2140@knanqh.ubzr>
On Wed, Jan 20, 2016 at 02:17:57PM -0500, Nicolas Pitre wrote:
> > It is also a friggin pointless /1000. The cpuidle code also loves to do
> > this, and its silly, u64 add/sub are _way_ cheaper than u64 / 1000.
>
> For the purpose of this code, nanoseconds simply provides too many bits
> for what we care. Computing the variance implies squared values.
>
> *However* we can simply do diff = (timestamp - w->timestamp) >> 10
> instead. No need to have an exact microsecs base.
Right, you could also reduce bits at the variance computation, but yes.
next prev parent reply other threads:[~2016-01-20 19:29 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-06 15:22 [RFC PATCH 0/2] IRQ based next prediction Daniel Lezcano
2016-01-06 15:22 ` [RFC PATCH 1/2] irq: Add a framework to measure interrupt timings Daniel Lezcano
2016-01-08 15:31 ` Thomas Gleixner
2016-01-12 11:42 ` Daniel Lezcano
2016-01-06 15:22 ` [RFC PATCH 2/2] sched: idle: IRQ based next prediction for idle period Daniel Lezcano
2016-01-06 17:40 ` Nicolas Pitre
2016-01-07 15:42 ` Daniel Lezcano
2016-01-12 19:27 ` Nicolas Pitre
2016-01-10 22:37 ` Daniel Lezcano
2016-01-10 22:46 ` Nicolas Pitre
2016-01-10 22:58 ` Daniel Lezcano
2016-01-10 23:13 ` Nicolas Pitre
2016-01-08 15:43 ` Thomas Gleixner
2016-01-12 12:41 ` Daniel Lezcano
2016-01-12 13:42 ` Thomas Gleixner
2016-01-12 14:16 ` Daniel Lezcano
2016-01-12 14:26 ` Thomas Gleixner
2016-01-12 14:52 ` Daniel Lezcano
2016-01-12 15:12 ` Thomas Gleixner
2016-01-12 16:04 ` Daniel Lezcano
2016-01-13 9:17 ` Thomas Gleixner
2016-01-18 13:21 ` Daniel Lezcano
2016-01-20 15:41 ` Thomas Gleixner
2016-01-20 16:00 ` [RFC V2 0/2] IRQ based next prediction Daniel Lezcano
2016-01-20 16:00 ` [RFC V2 1/2] irq: Add a framework to measure interrupt timings Daniel Lezcano
2016-01-20 17:55 ` Thomas Gleixner
2016-01-21 9:25 ` Daniel Lezcano
2016-01-21 10:27 ` Thomas Gleixner
2016-01-20 19:07 ` Peter Zijlstra
2016-01-20 19:57 ` Thomas Gleixner
2016-01-20 20:04 ` Nicolas Pitre
2016-01-20 20:20 ` Peter Zijlstra
2016-01-20 20:22 ` Thomas Gleixner
2016-01-21 9:50 ` Daniel Lezcano
2016-01-21 10:08 ` Peter Zijlstra
2016-01-21 12:38 ` Daniel Lezcano
2016-01-21 20:27 ` Thomas Gleixner
2016-01-21 13:52 ` Thomas Gleixner
2016-01-21 14:19 ` Daniel Lezcano
2016-01-21 18:56 ` Thomas Gleixner
2016-01-22 10:15 ` Peter Zijlstra
2016-01-21 9:26 ` Daniel Lezcano
2016-01-20 19:28 ` Peter Zijlstra
2016-01-21 9:53 ` Daniel Lezcano
2016-01-20 16:00 ` [RFC V2 2/2] sched: idle: IRQ based next prediction for idle period Daniel Lezcano
2016-01-20 17:46 ` Nicolas Pitre
2016-01-20 18:44 ` Peter Zijlstra
2016-01-21 10:03 ` Daniel Lezcano
2016-01-20 19:02 ` Peter Zijlstra
2016-01-20 19:17 ` Nicolas Pitre
2016-01-20 19:29 ` Peter Zijlstra [this message]
2016-01-20 19:34 ` Peter Zijlstra
2016-01-20 19:40 ` Peter Zijlstra
2016-01-20 19:57 ` Nicolas Pitre
2016-01-20 20:22 ` Peter Zijlstra
2016-01-20 19:49 ` Thomas Gleixner
2016-01-21 13:54 ` Daniel Lezcano
2016-01-21 14:12 ` Thomas Gleixner
2016-01-20 16:00 ` [RFC V2 0/2] IRQ based next prediction Daniel Lezcano
2016-01-20 16:00 ` [RFC V2 1/2] irq: Add a framework to measure interrupt timings Daniel Lezcano
2016-01-20 16:00 ` [RFC V2 2/2] sched: idle: IRQ based next prediction for idle period Daniel Lezcano
2016-01-20 20:14 ` Nicolas Pitre
2016-01-21 13:04 ` Daniel Lezcano
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