Messages in this thread | | | From | Gene Heskett <> | Subject | Re: [REPORT] cfs-v4 vs sd-0.44 | Date | Tue, 24 Apr 2007 03:00:07 -0400 |
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On Tuesday 24 April 2007, Ingo Molnar wrote: >* Peter Williams <pwil3058@bigpond.net.au> wrote: >> > The cases are fundamentally different in behavior, because in the >> > first case, X hardly consumes the time it would get in any scheme, >> > while in the second case X really is CPU bound and will happily >> > consume any CPU time it can get. >> >> Which still doesn't justify an elaborate "points" sharing scheme. >> Whichever way you look at that that's just another way of giving X >> more CPU bandwidth and there are simpler ways to give X more CPU if it >> needs it. However, I think there's something seriously wrong if it >> needs the -19 nice that I've heard mentioned. > >Gene has done some testing under CFS with X reniced to +10 and the >desktop still worked smoothly for him.
As a data point here, and probably nothing to do with X, but I did manage to lock it up, solid, reset button time tonight, by wanting 'smart' to get done with an update session after amanda had started. I took both smart processes I could see in htop all the way to -19, but when it was about done about 3 minutes later, everything came to an instant, frozen, reset button required lockup. I should have stopped at -17 I guess. :(
>So CFS does not 'need' a reniced >X. There are simply advantages to negative nice levels: for example >screen refreshes are smoother on any scheduler i tried. BUT, there is a >caveat: on non-CFS schedulers i tried X is much more prone to get into >'overscheduling' scenarios that visibly hurt X's performance, while on >CFS there's a max of 1000-1500 context switches a second at nice -10. >(which, considering the cost of a context switch is well under 1% >overhead.) > >So, my point is, the nice level of X for desktop users should not be set >lower than a low limit suggested by that particular scheduler's author. >That limit is scheduler-specific. Con i think recommends a nice level of >-1 for X when using SD [Con, can you confirm?], while my tests show that >if you want you can go as low as -10 under CFS, without any bad >side-effects. (-19 was a bit too much) > >> [...] You might as well just run it as a real time process. > >hm, that would be a bad idea under any scheduler (including CFS), >because real time processes can starve other processes indefinitely. > > Ingo
-- 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) I have discovered that all human evil comes from this, man's being unable to sit still in a room. -- Blaise Pascal - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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