Re: [PATCH 3/4] sched: introduce synchronized idle injection

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/4] sched: introduce synchronized idle injection
Date	2015-11-18 14:00 +0100
Message-ID	<qwav7-2Zg-1@gated-at.bofh.it> (permalink)
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On Wed, Nov 18, 2015 at 12:27:04PM +0000, Morten Rasmussen wrote:
> On Wed, Nov 18, 2015 at 11:35:41AM +0100, Peter Zijlstra wrote:
> > On Wed, Nov 18, 2015 at 09:36:22AM +0100, Ingo Molnar wrote:
> > > What will such throttling do to latencies, as observed by user-space tasks? What's 
> > > the typical expected frequency of the throttling frequency that you are targeting?
> > 
> > The default has 5ms (iirc) of forced idle, so depending on what you do,
> > noticeable to outright painful.
> 
> IIUC, it is 5 ticks, not ms.

The code uses hrtimers (badly), this means there _should_ not be a tick
dependency.

> Which raises the question, doesn't that mean that we get disturbed four
> times on each cpu during the forced idle period? So idle injection only
> makes sense if the platform has package states with a target residency
> less than a jiffy. Or, do we enter NOHZ idle? I haven't looked closely
> enough to figure out yet.

The idea is to hit NOHZ.
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Thread

Re: [PATCH 3/4] sched: introduce synchronized idle injection Ingo Molnar <mingo@kernel.org> - 2015-11-18 09:40 +0100
  Re: [PATCH 3/4] sched: introduce synchronized idle injection Peter Zijlstra <peterz@infradead.org> - 2015-11-18 11:40 +0100
    Re: [PATCH 3/4] sched: introduce synchronized idle injection Morten Rasmussen <morten.rasmussen@arm.com> - 2015-11-18 13:30 +0100
      Re: [PATCH 3/4] sched: introduce synchronized idle injection Peter Zijlstra <peterz@infradead.org> - 2015-11-18 14:00 +0100
        Re: [PATCH 3/4] sched: introduce synchronized idle injection Morten Rasmussen <morten.rasmussen@arm.com> - 2015-11-18 15:10 +0100
          Re: [PATCH 3/4] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-18 16:00 +0100
            Re: [PATCH 3/4] sched: introduce synchronized idle injection Morten Rasmussen <morten.rasmussen@arm.com> - 2015-11-18 16:10 +0100
              Re: [PATCH 3/4] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-18 16:20 +0100
                Re: [PATCH 3/4] sched: introduce synchronized idle injection Thomas Gleixner <tglx@linutronix.de> - 2015-11-18 16:30 +0100
                Re: [PATCH 3/4] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-18 20:00 +0100
                Re: [PATCH 3/4] sched: introduce synchronized idle injection Morten Rasmussen <morten.rasmussen@arm.com> - 2015-11-18 17:10 +0100
    Re: [PATCH 3/4] sched: introduce synchronized idle injection Ingo Molnar <mingo@kernel.org> - 2015-11-27 10:20 +0100
  Re: [PATCH 3/4] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-18 15:20 +0100
    Re: [PATCH 3/4] sched: introduce synchronized idle injection Ingo Molnar <mingo@kernel.org> - 2015-11-27 10:20 +0100
  Re: [PATCH 3/4] sched: introduce synchronized idle injection Arjan van de Ven <arjan@linux.intel.com> - 2015-11-18 15:30 +0100

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