linux-kernel - Re: Future of NOHZ full/isolation development (was Re: [NOHZ] Remove scheduler_tick_max

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Message-ID: <20141112150651.GF21343@twins.programming.kicks-ass.net>
Date:	Wed, 12 Nov 2014 16:06:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Tejun Heo <tj@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@....qualcomm.com>,
	Hugh Dickins <hughd@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: Future of NOHZ full/isolation development (was Re: [NOHZ] Remove
 scheduler_tick_max_deferment)

On Wed, Nov 12, 2014 at 08:26:05PM +0530, Viresh Kumar wrote:
> On 12 November 2014 19:24, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > I'd rather leave that to tracepoints. Like trace_hrtimer_spurious().
> 
> Yeah, it was just to prove things right on the console without getting
> into traces.
> 
> > Or better yet: have trace_hrtimer_interrupt() which we can compare against
> > trace_hrtimer_expire_entry/exit() to check if any hrtimer callback have run
> > in the interrupt. This way we avoid workarounds like the above count.
> 
> Yeah, I also believe we better add this debug information to mainline kernel.
> I will try to get a patch for that soon.
> 
> Would it be recommended to add both trace points?
> i.e. trace_hrtimer_interrupt() and trace_hrtimer_spurious() 

I don't think you need to add anything. We already have tracepoints for
every single interrupt (and therefore also for the hrtimer one) and we
have expiry tracepoints.


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