On Sun, 2011-12-25 at 08:31 +0100, Mike Galbraith wrote:
> Guess I need to fight fire with fire. Make ticks jitter a little
> somehow, so they don't make itimer wakeup jitter a truckload when it
> collides with tick that is busy colliding with zillion other ticks.
Yup. Perfect is the enemy of good.
non-virgin:
vogelweide:/abuild/mike/:[1]# sh -c 'echo $$ > /cpusets/rtcpus/tasks;./jitter -c 63 -f 960 -p 99 -t 10 -d 300'
CPU63 priority: 99 timer freq: 960 Hz (1041666 ns) tolerance: 10 usecs, stats interval: 300 secs
jitter: 8.87 min: 3.08 max: 11.95 mean: 4.92 stddev: 0.56
4 > 10 us hits min: 11.01 max: 11.95 mean: 11.35 stddev: 0.37
jitter: 8.68 min: 3.09 max: 11.77 mean: 4.91 stddev: 0.56
2 > 10 us hits min: 11.10 max: 11.77 mean: 11.44 stddev: 0.33
jitter: 7.90 min: 3.12 max: 11.02 mean: 4.91 stddev: 0.56
1 > 10 us hits min: 11.02 max: 11.02 mean: 11.02 stddev: 0.00
virgin:
vogelweide:/abuild/mike/:[1]# sh -c 'echo $$ > /cpusets/rtcpus/tasks;./jitter -c 63 -f 960 -p 99 -t 10 -d 300'
CPU63 priority: 99 timer freq: 960 Hz (1041666 ns) tolerance: 10 usecs, stats interval: 300 secs
jitter: 68.30 min: 2.43 max: 70.72 mean: 6.22 stddev: 6.41
16668 > 10 us hits min: 11.00 max: 70.72 mean: 28.57 stddev: 13.08
jitter: 71.76 min: 2.56 max: 74.32 mean: 6.29 stddev: 6.61
17257 > 10 us hits min: 11.00 max: 74.32 mean: 28.95 stddev: 13.24
jitter: 70.51 min: 2.50 max: 73.01 mean: 6.17 stddev: 6.26
16368 > 10 us hits min: 11.00 max: 73.01 mean: 28.29 stddev: 12.76
I'm still colliding a bit, and overhead is still too high, but poking
tick in the eye with a sharp stick made it crawl under it's rock, so
methinks the tail has been pinned on the right donkey.
-Mike
64 core DL980 idling, nohz=1, cores 4-63 isolated
non-virgin:
top - 08:26:35 up 2:04, 2 users, load average: 0.00, 0.01, 0.41
Tasks: 1051 total, 2 running, 1049 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 7911876k total, 1004812k used, 6907064k free, 12836k buffers
Swap: 1959924k total, 0k used, 1959924k free, 802324k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ P COMMAND
22210 root 20 0 9680 2032 928 R 1 0.0 0:00.50 0 top
4 root -41 0 0 0 0 S 0 0.0 0:07.85 0 sirq-timer/0
22 root -41 0 0 0 0 S 0 0.0 0:13.24 1 sirq-timer/1
37 root -41 0 0 0 0 S 0 0.0 0:13.32 2 sirq-timer/2
51 root -41 0 0 0 0 S 0 0.0 0:12.29 3 sirq-timer/3
65 root -41 0 0 0 0 S 0 0.0 0:12.07 4 sirq-timer/4
79 root -41 0 0 0 0 S 0 0.0 0:12.20 5 sirq-timer/5
93 root -41 0 0 0 0 S 0 0.0 0:12.07 6 sirq-timer/6
121 root -41 0 0 0 0 S 0 0.0 0:12.32 8 sirq-timer/8
163 root -41 0 0 0 0 S 0 0.0 0:12.22 11 sirq-timer/11
177 root -41 0 0 0 0 S 0 0.0 0:12.22 12 sirq-timer/12
191 root -41 0 0 0 0 S 0 0.0 0:12.25 13 sirq-timer/13
205 root -41 0 0 0 0 S 0 0.0 0:12.21 14 sirq-timer/14
219 root -41 0 0 0 0 S 0 0.0 0:12.21 15 sirq-timer/15
233 root -41 0 0 0 0 S 0 0.0 0:13.54 16 sirq-timer/16
virgin:
top - 08:57:39 up 23 min, 1 user, load average: 0.00, 0.02, 0.10
Tasks: 468 total, 2 running, 466 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 7914276k total, 471268k used, 7443008k free, 84040k buffers
Swap: 1959924k total, 0k used, 1959924k free, 243072k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ P COMMAND
179 root RT 0 0 0 0 S 3 0.0 0:45.89 32 ksoftirqd/32
231 root RT 0 0 0 0 S 3 0.0 0:46.48 40 ksoftirqd/40
241 root RT 0 0 0 0 S 3 0.0 0:46.53 42 ksoftirqd/42
246 root RT 0 0 0 0 S 3 0.0 0:46.27 43 ksoftirqd/43
184 root RT 0 0 0 0 S 3 0.0 0:44.16 33 ksoftirqd/33
206 root RT 0 0 0 0 S 3 0.0 0:44.48 35 ksoftirqd/35
211 root RT 0 0 0 0 R 3 0.0 0:45.19 36 ksoftirqd/36
216 root RT 0 0 0 0 S 3 0.0 0:44.83 37 ksoftirqd/37
221 root RT 0 0 0 0 S 3 0.0 0:43.73 38 ksoftirqd/38
226 root RT 0 0 0 0 S 3 0.0 0:44.73 39 ksoftirqd/39
236 root RT 0 0 0 0 S 3 0.0 0:45.86 41 ksoftirqd/41
251 root RT 0 0 0 0 S 3 0.0 0:43.64 44 ksoftirqd/44
323 root RT 0 0 0 0 S 3 0.0 0:40.69 56 ksoftirqd/56
345 root RT 0 0 0 0 S 3 0.0 0:40.83 58 ksoftirqd/58
201 root RT 0 0 0 0 S 3 0.0 0:44.86 34 ksoftirqd/34
256 root RT 0 0 0 0 S 3 0.0 0:41.62 45 ksoftirqd/45
273 root RT 0 0 0 0 S 3 0.0 0:41.09 46 ksoftirqd/46
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