Messages in this thread | | | From | "Doug Smythies" <> | Subject | RE: [RFT][PATCH v5 0/7] sched/cpuidle: Idle loop rework | Date | Tue, 20 Mar 2018 10:15:30 -0700 |
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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
... Doug
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