Messages in this thread | | | Date | Fri, 15 Jan 1999 14:00:29 +0000 | From | Neil Conway <> | Subject | Re: [uPATCH] SMP scheduling fix (?) |
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Robert M. Hyatt wrote: > > On Fri, 15 Jan 1999, Rik van Riel wrote: > > > On Thu, 14 Jan 1999, Robert M. Hyatt wrote: > > > > > This would make a good discussion point, since it is a topic I am > > > highly interested in. Take a process whose nice value is 0. And > > > a process that has been niced to +10. What is the expectation there? > > > > The expectation is that the +10 niced program gets half the > > CPU time from the 'normal' process. > > ok... then '20'??? IE it would seem that that might be 1/4th using > the same 'what number is next in this series?' :) That's not bad,
Rather simpler than that... A nice value of 20 means you get about 1/20th as much as a process with a nice value of 0. 5% is too big for lots of things, and this is one of the reasons I like Rik et al.'s patches for sched_idle.
Does anyone know why Linus doesn't like sched_idle things? (*Does* he dislike them??).
Neil
PS: Having bravely said the above without checking, I foolishly decided to check. It wasn't the case. Running two CPU-hogs, one non-niced and the other "nice +20", I got not the 95/5 split (actually 20/21 vs. 1/21 was what I expected), but a roughly 91.5/8.5 split. This means that the niced process got about one eleventh of the CPU time.
This doesn't square with what I read in the source code. "nice +20" should give the niced process (i386 values here) ONE time-slice in every round, while the non-niced should have 20 timeslices.
Argh.
(That's on my 2.0.35 desktop box btw. Quick inspection suggests 2.1.131 is better behaved but not sure.)
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