On Thu, Mar 3, 2016 at 9:06 PM, Steve Muckle <steve.muc...@linaro.org> wrote: > On 03/03/2016 05:07 AM, Vincent Guittot wrote: >> I mainly want to prevent any useless and periodic frequency switch >> because of an utilization that changes with the current frequency (if >> frequency invariance is not used) and that can make the formula >> selects another frequency than the current one. That what i can see >> when testing it . >> >> Sorry for the late reply, i was trying to do some test on my board but >> was facing some crash issue (not link with your patchset). So i have >> done some tests and i can see such instable behavior. I have generated >> a load of 33% at max frequency (3ms runs every 9ms) and i can see the >> frequency that toggles without any good reason. Saying that, i can see >> similar thing with ondemand. > > FWIW I ran some performance numbers on my chromebook 2. Initially I > forgot to bring in the frequency invariance support but that yielded an > opportunity to see the impact of it. > > The tests below consist of a periodic workload. The OH (overhead) > numbers show how close the workload got to running as slow as fmin (100% > = as slow as powersave gov, 0% = as fast as perf gov). The OR (overrun) > number is the count of instances where the busy work exceeded the period. > > First a comparison of schedutil with and without frequency invariance. > Run and period are in milliseconds. > > scu (no inv) scu (w/inv) > run period busy % OR OH OR OH > 1 100 1.00% 0 79.72% 0 95.86% > 10 1000 1.00% 0 24.52% 0 71.61% > 1 10 10.00% 0 21.25% 0 41.78% > 10 100 10.00% 0 26.06% 0 47.96% > 100 1000 10.00% 0 6.36% 0 26.03% > 6 33 18.18% 0 15.67% 0 31.61% > 66 333 19.82% 0 8.94% 0 29.46% > 4 10 40.00% 0 6.26% 0 12.93% > 40 100 40.00% 0 6.93% 2 14.08% > 400 1000 40.00% 0 1.65% 0 11.58% > 5 9 55.56% 0 3.70% 0 7.70% > 50 90 55.56% 1 4.19% 6 8.06% > 500 900 55.56% 0 1.35% 5 6.94% > 9 12 75.00% 0 1.60% 56 3.59% > 90 120 75.00% 0 1.88% 21 3.94% > 900 1200 75.00% 0 0.73% 4 4.41% > > Frequency invariance causes schedutil overhead to increase noticeably. I > haven't dug into traces or anything. Perhaps this is due to the > algorithm overshooting then overcorrecting etc., I do not yet know.
So as I said, the formula I used didn't take invariance into account, so that's quite as expected. > Here is a comparison, with frequency invariance, of ondemand and > interactive with schedfreq and schedutil. The first two columns (run and > period) are omitted so the table will fit. > > ondemand interactive schedfreq schedutil > busy % OR OH OR OH OR OH OR OH > 1.00% 0 68.96% 0 100.04% 0 78.49% 0 95.86% > 1.00% 0 25.04% 0 22.59% 0 72.56% 0 71.61% > 10.00% 0 21.75% 0 63.08% 0 52.40% 0 41.78% > 10.00% 0 12.17% 0 14.41% 0 17.33% 0 47.96% > 10.00% 0 2.57% 0 2.17% 0 0.29% 0 26.03% > 18.18% 0 12.39% 0 9.39% 0 17.34% 0 31.61% > 19.82% 0 3.74% 0 3.42% 0 12.26% 0 29.46% > 40.00% 2 6.26% 1 12.23% 0 6.15% 0 12.93% > 40.00% 0 0.47% 0 0.05% 0 2.68% 2 14.08% > 40.00% 0 0.60% 0 0.50% 0 1.22% 0 11.58% > 55.56% 2 4.25% 5 5.97% 0 2.51% 0 7.70% > 55.56% 0 1.89% 0 0.04% 0 1.71% 6 8.06% > 55.56% 0 0.50% 0 0.47% 0 1.82% 5 6.94% > 75.00% 2 1.65% 1 0.46% 0 0.26% 56 3.59% > 75.00% 0 1.68% 0 0.05% 0 0.49% 21 3.94% > 75.00% 0 0.28% 0 0.23% 0 0.62% 4 4.41% > > Aside from the 2nd and 3rd tests schedutil is showing decreased > performance across the board. The fifth test is particularly bad. I guess you mean performance in terms of the overhead? Thanks, Rafael
