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Date: Mon, 23 Apr 2007 13:19:40 -0400 From: Gene Heskett <gene.heskett@...il.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Ingo Molnar <mingo@...e.hu>, Juliusz Chroboczek <jch@....jussieu.fr>, Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>, Bill Davidsen <davidsen@....com>, Willy Tarreau <w@....eu>, William Lee Irwin III <wli@...omorphy.com>, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>, Arjan van de Ven <arjan@...radead.org>, Peter Williams <pwil3058@...pond.net.au>, Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr Subject: Re: [report] renicing X, cfs-v5 vs sd-0.46 On Monday 23 April 2007, Linus Torvalds wrote: >On Mon, 23 Apr 2007, Ingo Molnar wrote: >> You are completely right in the case of traditional schedulers. > >And apparently I'm completely right with CFS too. > >> Using CFS-v5, with Xorg at nice 0, the context-switch rate is low: >> >> procs -----------memory---------- ---swap-- -----io---- --system-- >> -----cpu------ r b swpd free buff cache si so bi bo in >> cs us sy id wa st 2 0 0 472132 13712 178604 0 0 0 32 >> 113 170 83 17 0 0 0 2 0 0 472172 13712 178604 0 0 0 >> 0 112 184 85 15 0 0 0 2 0 0 472196 13712 178604 0 0 >> 0 0 108 162 83 17 0 0 0 1 0 0 472076 13712 178604 0 >> 0 0 0 115 189 86 14 0 0 0 > >Around 170 context switches per second. > >> Renicing X to -10 increases context-switching, but not dramatically so, >> because it is throttled by CFS: >> >> procs -----------memory---------- ---swap-- -----io---- --system-- >> -----cpu------ r b swpd free buff cache si so bi bo in >> cs us sy id wa st 4 0 0 475752 13492 176320 0 0 0 64 >> 116 1498 85 15 0 0 0 4 0 0 475752 13492 176320 0 0 0 >> 0 107 1488 84 16 0 0 0 4 0 0 475752 13492 176320 0 0 >> 0 0 140 1514 86 14 0 0 0 4 0 0 475752 13492 176320 0 >> 0 0 0 107 1477 85 15 0 0 0 4 0 0 475752 13492 176320 >> 0 0 0 0 122 1498 84 16 0 0 0 > >Did you even *look* at your own numbers? Maybe you looked at "interrpts". >The context switch numbers go from 170 per second, to 1500 per second! > >If that's not "dramatically so", I don't know what is! Just how many >orders of magnitude worse does it have to be, to be "dramatic"? Apparently >one order of magnitude isn't "dramatic"? > >So you were wrong. The fact that it was still "usable" is a good >indication, but how about just admitting that you were wrong, and that >renicing X is the *WRONG*THING*TO*DO*. > >Just don't do it. It's wrong. It was wrong with the old schedulers, it's >wrong with the new scheduler, it's just WRONG. > >It was a hack, and it's a failed hack. And the fact that you don't seem to >realize that it's a failure, even when your OWN numbers clearly show that >it's failed, is a bit scary. > > Linus This message prompted me to do some checking in re context switches myself, and I've come to the conclusion that there could be a bug in vmstat itself. Run singly the context switching is reasonable even for a -19 niceness of x, its only showing about 200 or so on the first loop of vmstat. But throw in the -n 1 arguments and it goes crazy on the second and subsequent loops. X nice=0 [root@...ote ~]# vmstat -n 1 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 3 0 324 62836 37952 518080 0 0 786 446 474 201 10 4 82 4 0 0 0 324 62712 37952 518080 0 0 0 0 1309 2361 2 5 93 0 0 2 0 324 62712 37952 518080 0 0 0 0 1275 2203 2 4 94 0 0 0 0 324 62744 37952 518080 0 0 0 0 1305 2224 1 2 97 0 0 0 0 324 62744 37952 518080 0 0 0 0 1291 2232 0 1 99 0 0 X nice=-10 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 3 0 324 62432 38052 518080 0 0 784 445 476 205 10 4 82 4 0 0 0 324 62432 38052 518080 0 0 0 0 1190 3223 1 1 98 0 0 2 0 324 62440 38052 518080 0 0 0 0 1209 3210 2 3 95 0 0 0 0 324 62316 38060 518080 0 0 0 232 1201 3355 3 4 92 1 0 2 0 324 62316 38060 518080 0 0 0 0 1207 2794 1 2 97 0 0 X nice=10 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 4 0 324 62372 38184 518132 0 0 783 445 477 209 10 4 82 4 0 0 0 324 62372 38192 518132 0 0 0 272 1318 2262 0 3 97 0 0 0 0 324 62372 38192 518132 0 0 0 0 1293 2249 1 4 95 0 0 0 0 324 62248 38192 518132 0 0 0 0 1280 2443 4 2 94 0 0 0 0 324 62248 38192 518132 0 0 0 4 1294 2272 0 3 97 0 0 Now, I have NDI which set of figures is the true set, but please note that in all 3 cases the reported values for cs didn't scale up and down all that much if separated out into 1st pass, and subsequent passes. And, even with X nice=10, the system is still fairly smooth and usable. This is with 2.6.21-rc7-CFS-v5 I built late last evening. At Xnice=10 I just played a game of patience to watch the card animations and they were absolutely acceptably smooth. (and I won it in about 112 moves :) >From this users viewpoint, it (cfs-v5) works, and works very well indeed, and it deserves a place as one of 3 selectable options in mainline. The other 2 being the existing mainline way, & Con K's sd-0.45 or later. Both of these seem to be very large enhancements to the user experience over current mainline, which I'd discuss in terms borrowed from Joanne Dow. Comparatively speaking, mainline has a very high vacuum. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Jayne: "Let's move this conversation in a not-Jayne's-fault direction." --Episode #14, "Objects in Space" - 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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