Messages in this thread | | | From | "Doug Smythies" <> | Subject | RE: [RFT][PATCH v5 0/7] sched/cpuidle: Idle loop rework | Date | Wed, 21 Mar 2018 06:51:13 -0700 |
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On 2018.03.20 23:33 Rafael J. Wysocki wrote: > On Tuesday, March 20, 2018 10:03:50 PM CET Doug Smythies wrote: >> Summary: My results with kernel 4.16-rc6 and V8 of the patch set >> are completely different, and now show no clear difference >> (a longer test might reveal something). > > Does this mean that you see the "powernightmares" pattern with the v8 > again or are you referring to something else?
Sorry for not being clear. I do not see any "powernightmares" at all with V8.
After this e-mail I did a 3 hour trace and saw none.
>> On 2018.03.20 10:16 Doug Smythies wrote: >>> On 2018.03.20 03:02 Thomas Ilsche wrote: >>> >>>...[snip]... >>> >>>> Consider the Skylake server system which has residencies in C1E of >>>> 20 us and C6 of 800 us. I use a small while(1) {usleep(300);} >>>> unsynchronized pinned to each core. While this is an artificial >>>> case, it is a very innocent one - easy to predict and regular. Between >>>> vanilla 4.16.0-rc5 and idle-loop/v6, the power consumption increases >>>> from 149.7 W to 158.1 W. On 4.16.0-rc5, the cores sleep almost >>>> entirely in C1E. With the patches applied, the cores spend ~75% of >>>> their sleep time in C6, ~25% in C1E. The average time/usage for C1E is >>>> also lower with v6 at ~350 us rather than the ~550 us in C6 (and in >>>> C1E with the baseline). Generally the new menu governor seems to chose >>>> C1E if the next timer is an enabled sched timer - which occasionally >>>> interrupts the sleep-interval into two C1E sleeps rather than one C6. >>>> >>>> Manually disabling C6, reduces power consumption back to 149.5 W. >>> >>> ...[snip]... >>> >>> Note that one of the tests that I normally do is a work/sleep >>> frequency sweep from 100 to 2100 Hz, typically at a lowish >>> workload. I didn't notice anything odd with this test: >>> >>> http://fast.smythies.com/rjw_freq_sweep.png > > Would it be possible to produce this graph with the v8 of the > patchset?
Yes, sure.
>>> However, your test is at 3333 Hz (well, minus overheads). >>> I did the same as you. And was surprised to confirm >>> your power findings. In my case package power goes from >>> ~8.6 watts to ~7.3 watts with idle state 4 (C6) disabled. >>> >>> I am getting different residency times than you though. >>> I also observe different overheads between idle state 4 >>> being disabled or not. i.e. my actual loop frequency >>> drops from ~2801 Hz to ~2754 Hz. >>> >>> Example residencies over the previous minute: >>> >>> Idle state 4 (C6) disabled (seconds): >>> >>> Idle state 0: 0.001119 >>> Idle state 1: 0.056638 >>> Idle state 2: 13.100550 >>> Idle state 3: 446.266744 >>> Idle state 4: 0.000000 >>> >>> Idle state 4 (C6) enabled (seconds): >>> >>> Idle state 0: 0.034502 >>> Idle state 1: 1.949595 >>> Idle state 2: 78.291793 >>> Idle state 3: 96.467974 >>> Idle state 4: 286.247524 >> >> Now, with kernel 4.16-rc6 and V8 of the patch set and the poll fix >> I am unable to measure the processor package power difference >> between idle state 0 enabled or disabled (i.e. it is in the noise). >> also the loop time changes (overhead changes) are minimal. However, >> the overall loop time has dropped to ~2730 Hz, so there seems to be >> a little more overhead in general. >> >> I increased my loop frequency to ~3316 Hz. Similar. >> >> I increased my loop frequency to ~15474 Hz. Similar. >> Compared to a stock 4.16-rc6 kernel: The loop rate dropped >> to 15,209 Hz and it (the stock kernel) used about 0.3 more >> watts (out of 10.97, or ~3% more). > > So do you prefer v6 or v8? I guess the former?
Again sorry for not being clear. I was saying that V8 is great.
I did more tests after the original e-mail was sent, and the noted slight overhead drop was not always there (i.e. it was inconsistent).
... Doug
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