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Message-ID: <483F207D.4010908@nortel.com> Date: Thu, 29 May 2008 15:30:37 -0600 From: "Chris Friesen" <cfriesen@...tel.com> To: vatsa@...ux.vnet.ibm.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? Srivatsa Vaddagiri wrote: > In summary, can you do this before running your tests: > > 1. Apply updated patch below on top of 2.6.26-rc3 + Peter's patches > (http://programming.kicks-ass.net/kernel-patches/sched-smp-group-fixes/) I updated with the old set of patches you sent me, plus your patch. > 2. Setup test env as below: Done. 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. 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? I have people that are looking for within 4% fairness over a 1sec interval. 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. 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: 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 Chris -- 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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