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Date: Fri, 30 May 2008 17:06:53 +0530 From: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> To: "Chris Friesen" <cfriesen@...tel.com> Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, a.p.zijlstra@...llo.nl, pj@....com, Balbir Singh <balbir@...ibm.com>, aneesh.kumar@...ux.vnet.ibm.com, dhaval@...ux.vnet.ibm.com Subject: Re: fair group scheduler not so fair? On Thu, May 29, 2008 at 03:30:37PM -0600, Chris Friesen wrote: > Overall the group scheduler results look better, but I'm seeing an odd > scenario within a single group where sometimes I get a 67/67/66 breakdown > but sometimes it gives 100/50/50. Hmm ..I cant recreate this 100/50/50 situation (tried about 10 times). > Also, although the long-term results are good, the shorter-term fairness > isn't great. Is there a tuneable that would allow for a tradeoff between > performance and fairness? The tuneables I can think of are: - HZ (higher the better) - min/max_interval and imbalance_pct for each domain (lower the better) > I have people that are looking for within 4% fairness over a 1sec interval. That seems to be pretty difficult to achieve with the per-cpu runqueue and smpnice based load balancing approach we have now. > Initially I tried a simple setup with three hogs all in the default "sys" > group. Over multiple retries using 10-sec intervals, sometimes it gave > roughly 67% for each task, other times it settled into a 100/50/50 split > that remained stable over time. Was this with imbalance_pct set to 105? Does it make any difference if you change imbalance_pct to say 102? > 3 tasks in sys > 2471 cfriesen 20 0 3800 392 336 R 99.9 0.0 0:29.97 cat > 2470 cfriesen 20 0 3800 392 336 R 50.3 0.0 0:17.83 cat > 2469 cfriesen 20 0 3800 392 336 R 49.6 0.0 0:17.96 cat > > retry > 2475 cfriesen 20 0 3800 392 336 R 68.3 0.0 0:28.46 cat > 2476 cfriesen 20 0 3800 392 336 R 67.3 0.0 0:28.24 cat > 2474 cfriesen 20 0 3800 392 336 R 64.3 0.0 0:28.73 cat > > 2476 cfriesen 20 0 3800 392 336 R 67.1 0.0 0:41.79 cat > 2474 cfriesen 20 0 3800 392 336 R 66.6 0.0 0:41.96 cat > 2475 cfriesen 20 0 3800 392 336 R 66.1 0.0 0:41.67 cat > > retry > 2490 cfriesen 20 0 3800 392 336 R 99.7 0.0 0:22.23 cat > 2489 cfriesen 20 0 3800 392 336 R 49.9 0.0 0:21.02 cat > 2491 cfriesen 20 0 3800 392 336 R 49.9 0.0 0:13.94 cat > > > With three groups, one task in each, I tried both 10 and 60 second > intervals. The longer interval looked better but was still up to 0.8% off: I honestly don't know if we can do better than 0.8%! In any case, I'd expect that it would require more drastic changes. > 10-sec > 2490 cfriesen 20 0 3800 392 336 R 68.9 0.0 1:35.13 cat > 2491 cfriesen 20 0 3800 392 336 R 65.8 0.0 1:04.65 cat > 2489 cfriesen 20 0 3800 392 336 R 64.5 0.0 1:26.48 cat > > 60-sec > 2490 cfriesen 20 0 3800 392 336 R 67.5 0.0 3:19.85 cat > 2491 cfriesen 20 0 3800 392 336 R 66.3 0.0 2:48.93 cat > 2489 cfriesen 20 0 3800 392 336 R 66.2 0.0 3:10.86 cat > > > Finally, a more complicated scenario. three tasks in A, two in B, and one > in C. The 60-sec trial was up to 0.8 off, while a 3-second trial (just for > fun) was 8.5% off. > > 60-sec > 2491 cfriesen 20 0 3800 392 336 R 65.9 0.0 5:06.69 cat > 2499 cfriesen 20 0 3800 392 336 R 33.6 0.0 0:55.35 cat > 2490 cfriesen 20 0 3800 392 336 R 33.5 0.0 4:47.94 cat > 2497 cfriesen 20 0 3800 392 336 R 22.6 0.0 0:38.76 cat > 2489 cfriesen 20 0 3800 392 336 R 22.2 0.0 4:28.03 cat > 2498 cfriesen 20 0 3800 392 336 R 22.2 0.0 0:35.13 cat > > 3-sec > 2491 cfriesen 20 0 3800 392 336 R 58.2 0.0 13:29.60 cat > 2490 cfriesen 20 0 3800 392 336 R 34.8 0.0 9:07.73 cat > 2499 cfriesen 20 0 3800 392 336 R 31.0 0.0 5:15.69 cat > 2497 cfriesen 20 0 3800 392 336 R 29.4 0.0 3:37.25 cat > 2489 cfriesen 20 0 3800 392 336 R 23.3 0.0 7:26.25 cat > 2498 cfriesen 20 0 3800 392 336 R 23.0 0.0 3:33.24 cat I ran with this configuration: HZ = 1000, min/max_interval = 1 imbalance_pct = 102 My 10-sec fairness looks like below (Error = 1.5%): PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ #C COMMAND 4549 root 20 0 1384 228 176 R 65.2 0.0 0:36.02 0 hogc 4547 root 20 0 1384 228 176 R 32.8 0.0 0:17.87 0 hogb 4548 root 20 0 1384 228 176 R 32.6 0.0 0:18.28 1 hogb 4546 root 20 0 1384 232 176 R 22.9 0.0 0:11.82 1 hoga 4545 root 20 0 1384 228 176 R 22.3 0.0 0:11.74 1 hoga 4544 root 20 0 1384 232 176 R 22.1 0.0 0:11.93 1 hoga 3-sec fairness (error = 2.3% ..sometimes went upto 6.7%) 4549 root 20 0 1384 228 176 R 69.0 0.0 1:33.56 1 hogc 4548 root 20 0 1384 228 176 R 32.7 0.0 0:46.74 1 hogb 4547 root 20 0 1384 228 176 R 29.3 0.0 0:47.16 0 hogb 4546 root 20 0 1384 232 176 R 22.3 0.0 0:30.80 0 hoga 4544 root 20 0 1384 232 176 R 20.3 0.0 0:30.95 0 hoga 4545 root 20 0 1384 228 176 R 19.4 0.0 0:31.17 0 hoga -- Regards, vatsa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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