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? > 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? > > 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?