Re: fair group scheduler not so fair?

From: Srivatsa Vaddagiri
Date: Fri May 30 2008 - 06:12:59 EST


On Fri, May 30, 2008 at 12:13:24PM +0530, Dhaval Giani wrote:
> > Also, although the long-term results are good, the shorter-term fairness
> > isn't great. Is there a tuneable that would allow for a tradeoff between
> > performance and fairness? I have people that are looking for within 4%
> > fairness over a 1sec interval.
> >
>
> How fair does smp fairness look for a !group scenario? I don't expect
> group schould be able to do much better.

Just tested this combo for !group case:

1 nice0 (weight = 1024)
2 nice3 (each weight = 526)
3 nice5 (each weight = 335)

You'd expect nice0 to get (on a 2 cpu system):

2 * 1024 / (1024 + 2*526 + 3*335) = 66.47

This is what I see over a 10sec interval (error = 6%):

4386 root 20 0 1384 228 176 R 60.4 0.0 3:06.75 1 nice0
4387 root 23 3 1384 232 176 R 37.9 0.0 1:57.03 0 nice3
4388 root 23 3 1384 228 176 R 37.9 0.0 1:57.24 0 nice3
4390 root 25 5 1384 228 176 R 24.1 0.0 1:14.62 0 nice5
4391 root 25 5 1384 228 176 R 19.8 0.0 1:01.26 1 nice5
4389 root 25 5 1384 228 176 R 19.7 0.0 1:01.12 1 nice5

Over 120sec interval (error still as high as 6%):

4386 root 20 0 1384 228 176 R 60.4 0.0 6:13.95 1 nice0
4388 root 23 3 1384 228 176 R 37.9 0.0 3:54.69 0 nice3
4387 root 23 3 1384 232 176 R 37.9 0.0 3:54.44 0 nice3
4390 root 25 5 1384 228 176 R 24.2 0.0 2:29.45 0 nice5
4391 root 25 5 1384 228 176 R 19.8 0.0 2:02.56 1 nice5
4389 root 25 5 1384 228 176 R 19.8 0.0 2:02.44 1 nice5

The high error could be because of interference from other tasks. Anyway I
dont think !group case is better at achieving fairness over shorter
intervals.


--
Regards,
vatsa
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