Messages in this thread | | | Date | Fri, 15 Jan 1999 15:08:03 +0100 (MET) | From | Gabriel Paubert <> | Subject | Re: [uPATCH] SMP scheduling fix (?) |
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On Fri, 15 Jan 1999, Neil Conway wrote:
> 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.
It furiously looks like an off by one error (or an < versus <= comparison, or a postfix versus prefix increment or decrement) which would give actually 2 and 21 slices rather than 1 and 20:
2/23 ~= 8.7 % 21/23 ~= 91.3 %
Gabriel.
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