On 2106.04.09 20:45 Rafael J. Wysocki wrote:
>On Sat, Apr 9, 2016 at 6:39 PM, Mike Galbraith wrote:
>>
>> Hm, setting gov=performance, and taking the average of 3 30 second
>> interval PkgWatt samples as pipe-test runs..
>>
>> 714KHz/28.03Ws = 25.46
>> 877KHz/30.28Ws = 28.96
>>
>> ..for pipe-test, the tradeoff look a bit more like red than green.
>
> Well, fair enough, but that's just pipe-test, and what about the
> people who don't see the performance gain and see the energy loss,
> like Doug?
Some numbers from my computer:
Pipe-test (100 seconds):
Kernel 4.6-rc2 gov=powersave:
Stock: 3.86 uSecs/loop and 3148.05 Joules
Reverted: 3.34 uSecs/loop and 3567.43 Joules
Reverted is 13% faster at a cost of 13% more energy.
Idle stats (done separately and for 20e6 loops)
State k46rc2-ps (sec) k46rc2-rev-ps(sec)
0.00 0.01 4.09
1.00 38.68 0.00
2.00 0.46 0.27
3.00 0.01 0.00
4.00 464.23 380.23
total 503.38 384.60
Kernel 4.6-rc2 gov=performance:
Stock: 3.89 uSecs/loop and 3154.72 Joules
Reverted: 3.25 uSecs/loop and 3445.90 Joules
Reverted is 16% faster at a cost of 9% more energy.
Idle stats (done separately and for 20e6 loops)
State k46rc2-pf (sec) k46rc2-rev-pf (sec)
0.00 0.00 1.43
1.00 38.89 0.04
2.00 2.08 0.03
3.00 0.01 0.01
4.00 463.05 381.54
total 504.03 383.05
9 incremental kernel compiles, with no changes:
(the reference test from last cycle):
(2000 seconds turbostat package energy sample time):
There is no detectable consistent change in compile times:
Kernel 4.6-rc2 gov=powersave:
Stock: 48557 Joules
Reverted: 65439 Joules
Reverted costs 34% more energy.
(note: this result is unusually high. There are variations test to test)
Kernel 4.6-rc2 gov=performance:
Stock: 49965 Joules
Reverted: 59232 Joules
Reverted costs 19% more energy.
(note: never tested gov=performance before)
Idle stats not re-done (we had several samples last cycle).
> Essentially, this trades performance gains in somewhat special
> workloads for increased energy consumption in idle. Those workloads
> need not be run by everybody, but idle is.
>
> That said I applied the patch you're complaining about mostly because
> the commit that introduced the change in question in 4.5 claimed that
> it wouldn't affect idle power on systems with reasonably fast C1, but
> that didn't pass the reality test. I'm not totally against restoring
> that change, but it would need to be based on very solid evidence.
... Doug
