Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection

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From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection
Date	Tue, 10 Nov 2015 18:10:01 +0100
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On Tue, Nov 10, 2015 at 08:50:55AM -0800, Jacob Pan wrote:
> On Tue, 10 Nov 2015 17:36:46 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > > The downside is that we need to restart the timers every time if
> > > user were to change injection parameters, i.e. duration and percent.
> > > Or do locking which might be too expensive. In the previous
> > > approach, it will naturally catch up the parameter change.  
> > 
> > Why? the timer will fire and observe the new value for reprogramming
> > the next period. All you need to do is to ensure whole values are
> > written/read -- ie. avoid load/store tearing.
> Different per CPU timer may intercept parameter changes at slightly
> different time, so there is a race condition such that some CPUs may
> catch the period change later by one period, which results in a correct
> period change but at a different time, i.e. out of sync.

Ah yes. So if the locking hurts I can come up with a lockless algorithm
for this. Shouldn't be too hard.
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Thread

[RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 01:30 +0100
  Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Peter Zijlstra <peterz@infradead.org> - 2015-11-10 14:30 +0100
    Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 15:10 +0100
      Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Peter Zijlstra <peterz@infradead.org> - 2015-11-10 16:00 +0100
        Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Peter Zijlstra <peterz@infradead.org> - 2015-11-10 17:40 +0100
          Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 18:00 +0100
            Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Peter Zijlstra <peterz@infradead.org> - 2015-11-10 18:10 +0100
              Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 18:20 +0100
        Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 17:40 +0100
    Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 19:50 +0100

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