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    SubjectRe: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting
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    On Thu, 2018-05-17 at 17:04 +0200, Juri Lelli wrote:
    > On 17/05/18 12:59, Juri Lelli wrote:
    > > On 16/05/18 18:31, Juri Lelli wrote:
    > > > On 16/05/18 17:47, Peter Zijlstra wrote:
    > > > > On Wed, May 16, 2018 at 05:19:25PM +0200, Juri Lelli wrote:
    > > > >
    > > > > > Anyway, FWIW I started testing this on a E5-2609 v3 and I'm
    > > > > > not seeing
    > > > > > hackbench regressions so far (running with schedutil
    > > > > > governor).
    > > > >
    > > > > https://en.wikipedia.org/wiki/Haswell_(microarchitecture)#Serve
    > > > > r_processors
    > > > >
    > > > > Lists the E5 2609 v3 as not having turbo at all, which is
    > > > > basically a
    > > > > best case scenario for this patch.
    > > > >
    > > > > As I wrote earlier today; when turbo exists, like say the 2699,
    > > > > then
    > > > > when we're busy we'll run at U=2.3/3.6 ~ .64, which might
    > > > > confuse
    > > > > things.
    > > >
    > > > Indeed. I was mostly trying to see if adding this to the tick
    > > > might
    > > > introduce noticeable overhead.
    > >
    > > Blindly testing on an i5-5200U (2.2/2.7 GHz) gave the following
    > >
    > > # perf bench sched messaging --pipe --thread --group 2 --loop 20000
    > >
    > >                       count       mean       std     min     50%   
    > >     95%       99%     max
    > > hostname
    > > kernel                                                             
    > >                 
    > > i5-5200U
    > > test_after    30.0  13.843433  0.590605  12.369  13.810  14.85635  
    > > 15.08205  15.127
    > >          test_before   30.0  13.571167  0.999798  12.228  13.302  1
    > > 5.57805  16.40029  16.690
    > >
    > > It might be interesting to see what happens when using a single CPU
    > > only?
    > >
    > > Also, I will look at how the util signals look when a single CPU is
    > > busy..
    >
    > And this is showing where the problem is (as you were saying [1]):
    >
    > https://gist.github.com/jlelli/f5438221186e5ed3660194e4f645fe93
    >
    > Just look at the plots (and ignore setup).
    >
    > First one (pid:4483) shows a single task busy running on a single
    > CPU,
    > which seems to be able to sustain turbo for 5 sec. So task util
    > reaches
    > ~1024.
    >
    > Second one (pid:4283) shows the same task, but running together with
    > other 3 tasks (each one pinned to a different CPU). In this case util
    > saturates at ~943, which is due to the fact that max freq is still
    > considered to be the turbo one. :/


    One more point to note. Even if we calculate some utilization based on
    the freq-invariant and arrive at a P-state, we will not be able to
    control any P-state in turbo region (not even as a cap) on several
    Intel processors using PERF_CTL MSRs.


    >
    > [1] https://marc.info/?l=linux-kernel&m=152646464017810&w=2

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