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Date: Mon, 30 Jul 2007 17:07:46 -0400 From: Chris Snook <csnook@...hat.com> To: tim.c.chen@...ux.intel.com CC: Andrea Arcangeli <andrea@...e.de>, mingo@...e.hu, linux-kernel@...r.kernel.org Subject: Re: pluggable scheduler thread (was Re: Volanomark slows by 80% under CFS) Tim Chen wrote: > On Sat, 2007-07-28 at 02:51 -0400, Chris Snook wrote: > >> Tim -- >> >> Since you're already set up to do this benchmarking, would you mind >> varying the parameters a bit and collecting vmstat data? If you want to >> run oprofile too, that wouldn't hurt. >> > > Here's the vmstat data. The number of runnable processes are > fewer and there're more contex switches with CFS. > > The vmstat for 2.6.22 looks like > > procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ > r b swpd free buff cache si so bi bo in cs us sy id wa st > 391 0 0 1722564 14416 95472 0 0 169 25 76 6520 3 3 89 5 0 > 400 0 0 1722372 14416 95496 0 0 0 0 264 641685 47 53 0 0 0 > 368 0 0 1721504 14424 95496 0 0 0 7 261 648493 46 51 3 0 0 > 438 0 0 1721504 14432 95496 0 0 0 2 264 690834 46 54 0 0 0 > 400 0 0 1721380 14432 95496 0 0 0 0 260 657157 46 53 1 0 0 > 393 0 0 1719892 14440 95496 0 0 0 6 265 671599 45 53 2 0 0 > 423 0 0 1719892 14440 95496 0 0 0 15 264 701626 44 56 0 0 0 > 375 0 0 1720240 14472 95504 0 0 0 72 265 671795 43 53 3 0 0 > 393 0 0 1720140 14480 95504 0 0 0 7 265 733561 45 55 0 0 0 > 355 0 0 1716052 14480 95504 0 0 0 0 260 670676 43 54 3 0 0 > 419 0 0 1718900 14480 95504 0 0 0 4 265 680690 43 55 2 0 0 > 396 0 0 1719148 14488 95504 0 0 0 3 261 712307 43 56 0 0 0 > 395 0 0 1719148 14488 95504 0 0 0 2 264 692781 44 54 1 0 0 > 387 0 0 1719148 14492 95504 0 0 0 41 268 709579 43 57 0 0 0 > 420 0 0 1719148 14500 95504 0 0 0 3 265 690862 44 54 2 0 0 > 429 0 0 1719396 14500 95504 0 0 0 0 260 704872 46 54 0 0 0 > 460 0 0 1719396 14500 95504 0 0 0 0 264 716272 46 54 0 0 0 > 419 0 0 1719396 14508 95504 0 0 0 3 261 685864 43 55 2 0 0 > 455 0 0 1719396 14508 95504 0 0 0 0 264 703718 44 56 0 0 0 > 395 0 0 1719372 14540 95512 0 0 0 64 265 692785 45 54 1 0 0 > 424 0 0 1719396 14548 95512 0 0 0 10 265 732866 45 55 0 0 0 > > While 2.6.23-rc1 look like > procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ > r b swpd free buff cache si so bi bo in cs us sy id wa st > 23 0 0 1705992 17020 95720 0 0 0 0 261 1010016 53 42 5 0 0 > 7 0 0 1706116 17020 95720 0 0 0 13 267 1060997 52 41 7 0 0 > 5 0 0 1706116 17020 95720 0 0 0 28 266 1313361 56 41 3 0 0 > 19 0 0 1706116 17028 95720 0 0 0 8 265 1273669 55 41 4 0 0 > 18 0 0 1706116 17032 95720 0 0 0 2 262 1403588 55 41 4 0 0 > 23 0 0 1706116 17032 95720 0 0 0 0 264 1272561 56 40 4 0 0 > 14 0 0 1706116 17032 95720 0 0 0 0 262 1046795 55 40 5 0 0 > 16 0 0 1706116 17032 95720 0 0 0 0 260 1361102 58 39 4 0 0 > 4 0 0 1706224 17120 95724 0 0 0 126 273 1488711 56 41 3 0 0 > 24 0 0 1706224 17128 95724 0 0 0 6 261 1408432 55 41 4 0 0 > 3 0 0 1706240 17128 95724 0 0 0 48 273 1299203 54 42 4 0 0 > 16 0 0 1706240 17132 95724 0 0 0 3 261 1356609 54 42 4 0 0 > 5 0 0 1706364 17132 95724 0 0 0 0 264 1293198 58 39 3 0 0 > 9 0 0 1706364 17132 95724 0 0 0 0 261 1555153 56 41 3 0 0 > 13 0 0 1706364 17132 95724 0 0 0 0 264 1160296 56 40 4 0 0 > 8 0 0 1706364 17132 95724 0 0 0 0 261 1388909 58 38 4 0 0 > 18 0 0 1706364 17132 95724 0 0 0 0 264 1236774 56 39 5 0 0 > 11 0 0 1706364 17136 95724 0 0 0 2 261 1360325 57 40 3 0 0 > 5 0 0 1706364 17136 95724 0 0 0 1 265 1201912 57 40 3 0 0 > 8 0 0 1706364 17136 95724 0 0 0 0 261 1104308 57 39 4 0 0 > 7 0 0 1705976 17232 95724 0 0 0 127 274 1205212 58 39 4 0 0 > > Tim > From a scheduler performance perspective, it looks like CFS is doing much better on this workload. It's spending a lot less time in %sys despite the higher context switches, and there are far fewer tasks waiting for CPU time. The real problem seems to be that volanomark is optimized for a particular scheduler behavior. That's not to say that we can't improve volanomark performance under CFS, but simply that CFS isn't so fundamentally flawed that this is impossible. When I initially agreed with zeroing out wait time in sched_yield, I didn't realize that it could be negative and that this would actually promote processes in some cases. I still think it's reasonable to zero out positive wait times. Can you test to see if that optimization does better than unconditionally zeroing them out? -- 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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