linux-kernel - Re: [RFC/RFT][PATCH v3 0/6] sched/cpuidle: Idle loop rework

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Message-ID: <3457137.VQn7spFdJh@aspire.rjw.lan>
Date:   Sat, 10 Mar 2018 10:00:08 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     'Rik van Riel' <riel@...riel.com>,
        'Mike Galbraith' <mgalbraith@...e.de>,
        'Thomas Gleixner' <tglx@...utronix.de>,
        'Paul McKenney' <paulmck@...ux.vnet.ibm.com>,
        'Thomas Ilsche' <thomas.ilsche@...dresden.de>,
        'Frederic Weisbecker' <fweisbec@...il.com>,
        'Linux PM' <linux-pm@...r.kernel.org>,
        'Aubrey Li' <aubrey.li@...ux.intel.com>,
        'LKML' <linux-kernel@...r.kernel.org>,
        'Peter Zijlstra' <peterz@...radead.org>
Subject: Re: [RFC/RFT][PATCH v3 0/6] sched/cpuidle: Idle loop rework

On Saturday, March 10, 2018 8:41:39 AM CET Doug Smythies wrote:
> On 2018.03.09 07:19 Rik van Riel wrote:
> > On Fri, 2018-03-09 at 10:34 +0100, Rafael J. Wysocki wrote:
> >> Hi All,
> >> 
> >> Thanks a lot for the discussion and testing so far!
> >> 
> >> This is a total respin of the whole series, so please look at it
> >> afresh.
> >> Patches 2 and 3 are the most similar to their previous versions, but
> >> still they are different enough.
> >
> > This series gives no RCU errors on startup,
> > and no CPUs seem to be getting stuck any more.
> 
> Confirmed on my test server. Boot is normal and no other errors, so far.

Thanks for testing, much appreciated!

> Part 1: Idle test:
> 
> I was able to repeat Mike's higher power issue under very light load,
> well no load in my case, with V2.
> 
> V3 is much better.
> 
> A one hour trace on my very idle server was 22 times smaller with V3
> than V2, and mainly due to idle state 4 not exiting and re-entering
> every tick time for great periods of time.
> 
> Disclaimer: From past experience, 1 hour is not nearly long enough
> for this test. Issues tend to come in bunches, sometimes many hours
> apart.
> 
> V2:
> Idle State 4: Entries: 1359560
> CPU: 0: Entries: 125305
> CPU: 1: Entries: 62489
> CPU: 2: Entries: 10203
> CPU: 3: Entries: 108107
> CPU: 4: Entries: 19915
> CPU: 5: Entries: 430253
> CPU: 6: Entries: 564650
> CPU: 7: Entries: 38638
> 
> V3:
> Idle State 4: Entries: 64505
> CPU: 0: Entries: 13060
> CPU: 1: Entries: 5266
> CPU: 2: Entries: 15744
> CPU: 3: Entries: 5574
> CPU: 4: Entries: 8425
> CPU: 5: Entries: 6270
> CPU: 6: Entries: 5592
> CPU: 7: Entries: 4574
> 
> Kernel 4.16-rc4:
> Idle State 4: Entries: 61390
> CPU: 0: Entries: 9529
> CPU: 1: Entries: 10556
> CPU: 2: Entries: 5478
> CPU: 3: Entries: 5991
> CPU: 4: Entries: 3686
> CPU: 5: Entries: 7610
> CPU: 6: Entries: 11074
> CPU: 7: Entries: 7466
> 
> With apologies to those that do not like the term "PowerNightmares",

OK, and what exactly do you count as "PowerNightmares"?

> it has become very ingrained in my tools:
> 
> V2:
> 1 hour idle Summary:
> 
> Idle State 0: Total Entries: 113 : PowerNightmares: 56 : Not PN time (seconds): 0.001224 : PN time: 65.543239 : Ratio: 53548.397792
> Idle State 1: Total Entries: 1015 : PowerNightmares: 42 : Not PN time (seconds): 0.053986 : PN time: 21.054470 : Ratio: 389.998703
> Idle State 2: Total Entries: 1382 : PowerNightmares: 17 : Not PN time (seconds): 0.728686 : PN time: 6.046906 : Ratio: 8.298370
> Idle State 3: Total Entries: 113 : PowerNightmares: 13 : Not PN time (seconds): 0.069055 : PN time: 6.021458 : Ratio: 87.198002

The V2 had a serious bug, please discard it entirely.

> 
> V3:
> 1 hour idle Summary: Average processor package power 3.78 watts
> 
> Idle State 0: Total Entries: 134 : PowerNightmares: 109 : Not PN time (seconds): 0.000477 : PN time: 144.719723 : Ratio: 303395.646541
> Idle State 1: Total Entries: 1104 : PowerNightmares: 84 : Not PN time (seconds): 0.052639 : PN time: 74.639142 : Ratio: 1417.943768
> Idle State 2: Total Entries: 968 : PowerNightmares: 141 : Not PN time (seconds): 0.325953 : PN time: 128.235137 : Ratio: 393.416035
> Idle State 3: Total Entries: 295 : PowerNightmares: 103 : Not PN time (seconds): 0.164884 : PN time: 97.159421 : Ratio: 589.259243
> 
> Kernel 4.16-rc4: Average processor package power (excluding a few minutes of abnormal power) 3.70 watts.
> 1 hour idle Summary:
> 
> Idle State 0: Total Entries: 168 : PowerNightmares: 59 : Not PN time (seconds): 0.001323 : PN time: 81.802197 : Ratio: 61830.836545
> Idle State 1: Total Entries: 1669 : PowerNightmares: 78 : Not PN time (seconds): 0.022003 : PN time: 37.477413 : Ratio: 1703.286509
> Idle State 2: Total Entries: 1447 : PowerNightmares: 30 : Not PN time (seconds): 0.502672 : PN time: 0.789344 : Ratio: 1.570296
> Idle State 3: Total Entries: 176 : PowerNightmares: 0 : Not PN time (seconds): 0.259425 : PN time: 0.000000 : Ratio: 0.000000
> 
> Part 2: 100% load on one CPU test. Test duration 4 hours
> 
> V3: Summary: Average processor package power 26.75 watts
> 
> Idle State 0: Total Entries: 10039 : PowerNightmares: 7186 : Not PN time (seconds): 0.067477 : PN time: 6215.220295 : Ratio: 92108.722903
> Idle State 1: Total Entries: 17268 : PowerNightmares: 195 : Not PN time (seconds): 0.213049 : PN time: 55.905323 : Ratio: 262.405939
> Idle State 2: Total Entries: 5858 : PowerNightmares: 676 : Not PN time (seconds): 2.578006 : PN time: 167.282069 : Ratio: 64.888161
> Idle State 3: Total Entries: 1500 : PowerNightmares: 488 : Not PN time (seconds): 0.772463 : PN time: 125.514015 : Ratio: 162.485472
> 
> Kernel 4.16-rc4: Summary: Average processor package power 27.41 watts
> 
> Idle State 0: Total Entries: 9096 : PowerNightmares: 6540 : Not PN time (seconds): 0.051532 : PN time: 7886.309553 : Ratio: 153037.133492
> Idle State 1: Total Entries: 28731 : PowerNightmares: 215 : Not PN time (seconds): 0.211999 : PN time: 77.395467 : Ratio: 365.074679
> Idle State 2: Total Entries: 4474 : PowerNightmares: 97 : Not PN time (seconds): 1.959059 : PN time: 0.874112 : Ratio: 0.446190
> Idle State 3: Total Entries: 2319 : PowerNightmares: 0 : Not PN time (seconds): 1.663376 : PN time: 0.000000 : Ratio: 0.000000
> 
> Graph of package power verses time: http://fast.smythies.com/rjwv3_100.png

The graph actually shows an improvement to my eyes, as the blue line is quite
consistently above the red one except for a few regions (and I don't really
understand the drop in the blue line by the end of the test window).

Thanks!