2.6.22.2-cfs-v19.1 stops honouring nice 3 after some hours

From: Michael Gerdau
Date: Wed Aug 15 2007 - 12:30:25 EST


Hi Ingo,

I played a bit with renicing my (mostly) CPU bound jobs and found
somewhat strange behaviour.

I'm on 2.6.22.2-cfs-v19.1 -- I can't boot into 2.6.23-rc3 as part of
my daily work because my NVIDIA driver doesn't yet work with it though
I could try to do some X-less testing if need be.

I'm running 4 CPU bound jobs, 2 of which are more important to me.
I therefor reniced the other 2 to level 3 and the CPU percentages
were roughly 66/66/33/33 on my Dualcore system. So far all fine.

Some 6 hours later I rechecked with top -d 60 and got the output below:

19629 mgd 20 0 334m 263m 2700 R 49 8.1 69:16.45 perl
29668 mgd 20 0 396m 262m 2700 R 49 8.0 112:17.21 perl
6933 mgd 23 3 96576 21m 3672 R 47 0.7 46:38.83 perl
14162 mgd 23 3 165m 28m 3672 R 47 0.9 194:55.31 perl

I reniced to 0:

19629 mgd 20 0 334m 263m 2700 R 48 8.1 71:02.86 perl
6933 mgd 20 0 96652 21m 3672 R 48 0.7 48:23.41 perl
14162 mgd 20 0 165m 28m 3676 R 48 0.9 196:39.81 perl
29668 mgd 20 0 396m 262m 2700 R 48 8.0 114:03.56 perl

...and back to 3 with no noticeable change.

[at this point job 14162 finished and was replaced by an similar
job 22558]

I then decided to do some statistics and reniced to 1:

29668 mgd 20 0 396m 262m 2700 R 48 8.0 115:24.12 perl
19629 mgd 20 0 334m 263m 2700 R 48 8.1 72:23.36 perl
22558 mgd 21 1 92184 17m 3672 R 48 0.5 0:56.81 perl
6933 mgd 21 1 96576 21m 3672 R 48 0.7 49:54.12 perl

Now I reniced to 2 and without knowing why, the ratios seem to be back
to where I want them.

29668 mgd 20 0 396m 262m 2700 R 59 8.0 116:33.98 perl
19629 mgd 20 0 334m 264m 2700 R 58 8.1 73:31.49 perl
22558 mgd 22 2 92220 17m 3672 R 37 0.5 1:46.99 perl
6933 mgd 22 2 96688 21m 3672 R 36 0.7 50:44.77 perl

Renicing to 3 again gives me what I want:

29668 mgd 20 0 397m 262m 2700 R 65 8.0 117:25.93 perl
19629 mgd 20 0 334m 264m 2700 R 63 8.1 74:21.84 perl
22558 mgd 23 3 92220 17m 3672 R 32 0.5 2:13.83 perl
6933 mgd 23 3 96652 21m 3672 R 32 0.7 51:11.24 perl


I don't know why I had the very first output above though.

Best,
Michael
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