Messages in this thread | | | From | "Doug Smythies" <> | Subject | RE: [RFT][PATCH v5 0/7] sched/cpuidle: Idle loop rework | Date | Tue, 20 Mar 2018 14:03:50 -0700 |
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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).
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 > > 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).
... Doug
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