On 2018.03.25 23:00 Doug Smythies wrote: > On 2018.03.25 14:25 Rik van Riel wrote: > On Sun, 2018-03-25 at 23:34 +0200, Rafael J. Wysocki wrote: >> On Sunday, March 25, 2018 10:15:52 PM CEST Rik van Riel wrote:
...[snip]... >>>> >>>> OK, I am still seeing a performance >>>> degradation with the above, though >>>> not throughout the entire workload. >>>> >>>> It appears that making the idle loop >>>> do anything besides cpu_relax() for >>>> a significant amount of time slows >>>> things down. >>> >>> I see. > > I have no proof, but I do not see that as > the problem. > > I think the issue is the overall exiting > and then re-entering idle state 0 much > more often, and the related overheads, where > interrupts are disabled for short periods. > > My jury rigged way of trying to create similar > conditions seems to always have the ISR return with > the need_resched() flag set, so there is no difference > in idle state 0 entries per unit time between kernel > 4.16-rc6 and one with the poll fixes added. > > i.e. the difference between these numbers over some time: > > cat /sys/devices/system/cpu/cpu*/cpuidle/state0/usage > > Rik, I wonder if you see a difference with your real > workflow? Using iperf, I was able to show a difference on my computer. Another computer was used as the server, and my test computer was the client. (the other way around didn't show a difference) With Kernel 4.16-rc6 I got about ~2000 idle state 0 entries per minute and ~155 seconds residency. ~32 watts package power. With the poll stuff included I got ~46000 idle state 0 entries per minute and ~53 seconds residency. ~20 watts package power. ... Doug
