linux-kernel - Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings

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Message-ID: <20160120202014.GK6356@twins.programming.kicks-ass.net>
Date:	Wed, 20 Jan 2016 21:20:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>, rafael@...nel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	nicolas.pitre@...aro.org, vincent.guittot@...aro.org
Subject: Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings

On Wed, Jan 20, 2016 at 08:57:06PM +0100, Thomas Gleixner wrote:
> > Here too, ktime_get() is daft.
> 
> What's the problem? ktime_xxx() itself or just the clock monotonic variant?
> 
> On 99.9999% of the platforms ktime_get_mono_fast/raw_fast is not any slower
> than sched_clock(). The only case where sched_clock is faster is if your TSC
> is buggered and the box switches to HPET for timekeeping.

The HPET thing, I just don't want to have to explain why this is so much
more expensive on some random weird machine, esp. since it really
doesn't matter.