From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicolas Pitre Subject: Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings Date: Wed, 20 Jan 2016 15:04:55 -0500 (EST) Message-ID: References: <1453305636-22156-1-git-send-email-daniel.lezcano@linaro.org> <1453305636-22156-2-git-send-email-daniel.lezcano@linaro.org> <20160120190718.GS6357@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Thomas Gleixner Cc: Peter Zijlstra , Daniel Lezcano , rafael@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, vincent.guittot@linaro.org List-Id: linux-pm@vger.kernel.org On Wed, 20 Jan 2016, Thomas Gleixner wrote: > On Wed, 20 Jan 2016, Peter Zijlstra wrote: > > > On Wed, Jan 20, 2016 at 05:00:32PM +0100, Daniel Lezcano wrote: > > > +++ b/kernel/irq/handle.c > > > @@ -165,6 +165,7 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc) > > > /* Fall through to add to randomness */ > > > case IRQ_HANDLED: > > > flags |= action->flags; > > > + handle_irqtiming(irq, action->dev_id); > > > break; > > > > > > default: > > > > > +++ b/kernel/irq/internals.h > > > > > +static inline void handle_irqtiming(unsigned int irq, void *dev_id) > > > +{ > > > + if (__irqtimings->handler) > > > + __irqtimings->handler(irq, ktime_get(), dev_id); > > > +} > > > > 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. > > But I wonder, whether this couldn't do with jiffies in the first place. If the > interrupt comes faster than a jiffie then you hardly go into some interesting > power state, but I might be wrong as usual :) Jiffies are not precise enough for some power states, even more so with HZ = 100 on many platforms. Nicolas