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SubjectRe: 'autogroup' sched code KILLING responsiveness
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On Fri, 2011-01-21 at 10:20 -0800, Michael Witten wrote:
> Bisecting shows that this commit:
>
> 5091faa449ee0b7d73bc296a93bca9540fc51d0a
> sched: Add 'autogroup' scheduling feature: automated per session task groups
> Date: Tue Nov 30 14:18:03 2010 +0100
>
> is the reason that my computer has become unusable.
>
> With that code in place, a resource-intensive activity (such as
> compiling the Linux kernel) causes my computer to become
> unresponsive for many seconds at a time; the entire screen
> does not refresh, typed keys are dropped or are handled very
> late, etc (even in Linux's plain virtual consoles).

That's not what I'm experiencing with a UP kernel...

marge:~> time perf stat -a sh -c 'true'

Performance counter stats for 'sh -c true':

49580 cache-misses # 5.170 M/sec (scaled from 37.28%)
336112 cache-references # 35.048 M/sec (scaled from 78.81%)
185857 branch-misses # 21.019 % (scaled from 62.83%)
884249 branches # 92.204 M/sec (scaled from 21.25%)
12672552 instructions # 0.553 IPC (scaled from 58.38%)
22896301 cycles # 2387.490 M/sec (scaled from 58.38%)
410 page-faults # 0.043 M/sec
0 CPU-migrations # 0.000 M/sec
13 context-switches # 0.001 M/sec
9.590115 task-clock-msecs # 1.005 CPUs

0.009540836 seconds time elapsed


real 0m0.020s
user 0m0.000s
sys 0m0.000s
marge:~>

It took 20 ms to do the above and get it to my screen while the below
was running (among others). I've got a make -j 100 running as I write
this, and don't even notice that it's running.

Can you provide some information such as hardware description,
configuration, and perhaps measurements demonstrating the problem?

top - 22:34:38 up 33 min, 22 users, load average: 104.07, 101.73, 78.13
Tasks: 675 total, 101 running, 574 sleeping, 0 stopped, 0 zombie
Cpu(s): 95.2%us, 4.8%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ P COMMAND
6770 root 20 0 401m 79m 29m R 46.9 1.0 3:22.66 0 mplayer
6100 root 20 0 449m 94m 18m S 2.9 1.2 1:33.82 0 Xorg
7486 root 20 0 374m 46m 17m S 2.9 0.6 0:54.02 0 konsole
7752 root 20 0 104m 66m 8072 R 1.0 0.8 0:01.76 0 cc1
9796 root 20 0 89764 49m 8028 R 1.0 0.6 0:01.21 0 cc1
9928 root 20 0 98916 59m 8164 R 1.0 0.7 0:01.18 0 cc1
10321 root 20 0 88788 49m 8116 R 1.0 0.6 0:01.06 0 cc1
10619 root 20 0 89736 50m 8068 R 1.0 0.6 0:01.00 0 cc1
11356 root 20 0 19764 8152 2300 S 1.0 0.1 0:00.01 0 as
11597 root 20 0 97212 56m 7924 R 1.0 0.7 0:00.65 0 cc1
12203 root 20 0 79332 40m 7588 R 1.0 0.5 0:00.48 0 cc1
12209 root 20 0 80760 40m 7536 R 1.0 0.5 0:00.47 0 cc1
12247 root 20 0 85252 46m 7752 R 1.0 0.6 0:00.46 0 cc1
12510 root 20 0 82192 40m 5184 R 1.0 0.5 0:00.36 0 cc1
12612 root 20 0 81172 39m 5192 R 1.0 0.5 0:00.33 0 cc1
12615 root 20 0 81160 38m 4360 R 1.0 0.5 0:00.33 0 cc1





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