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. 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. The catch is that I do not have power numbers to go with this data, as I'm not currently equipped to gather them. So more analysis is definitely needed to capture the full story. thanks, Steve -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
