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SubjectRe: 2.4.17 absurd number of context switches
Is your system heavy loaded?
I'm running Postgres 7.1.2 on 2-way x86 too and noticed that context switches
are high!
Here the slice on about %50 free cpu time, but when goes up to %80-%90 -
context switches going to 10000-15000:
procs memory swap io system
cpu
r b w swpd free buff cache si so bi bo in cs us sy
id
1 0 0 87364 15448 2540 1218324 1 1 20 13 7 17 16 4
18
3 0 0 87364 12596 2552 1219336 36 0 964 0 504 1385 30 16
53
4 1 0 87364 7684 2556 1220568 0 0 1196 768 687 1645 28 16
56
2 1 0 87364 6172 2568 1218940 0 0 1156 0 604 1485 31 11
58
10 0 0 87364 5648 2572 1218764 0 0 972 0 366 1012 23 18
60
5 0 0 87364 6216 2580 1218208 0 0 604 0 411 1154 28 20
52
12 0 0 87364 5832 2580 1216952 0 0 272 0 317 1567 31 23
46
12 0 0 87364 6048 2592 1216100 0 0 168 384 448 2011 47 13
40
11 0 0 87364 5920 2596 1216116 0 0 20 0 284 2307 58 12
30
9 0 0 87364 6556 2600 1216136 0 0 12 0 284 2164 53 9
38
11 0 0 87364 6536 2608 1216220 0 0 68 0 324 2140 50 12
38
23 0 0 87364 7176 2612 1216232 0 0 4 0 317 2238 46 9
46
12 0 0 87364 6880 2616 1216360 16 0 140 256 440 2367 33 18
49
9 0 0 87364 6380 2644 1216692 0 0 336 0 454 2874 28 17
55
7 0 0 87364 5956 2648 1216772 0 0 52 0 550 2659 28 17
55
1 0 0 87364 5420 2628 1215544 0 0 32 0 538 648 13 2
85
0 0 0 87364 6180 2632 1215636 0 0 72 0 421 430 11 3
86
0 0 0 87364 6152 2632 1215664 0 0 20 1152 328 225 6 1
92
0 0 0 87364 6116 2632 1215696 0 0 36 0 278 242 7 1
91
0 0 0 87364 5512 2580 1214524 0 0 152 0 433 426 10 4
87
0 0 0 87364 9072 2580 1214536 0 0 8 0 303 290 8 1
91


"Jeffrey W. Baker" wrote:

> Here's a slice of vmstat 1 on my 2-way x86, 2GB main memory machine
> running Postgres 7.2beta4 on Linux 2.4.17:
> cpu
> r b w bi bo in cs us sy id
> 7 0 0 371612 58272 18576 1568896 0 0 0 168 414 33113 49 38 13
> 9 0 0 371612 59168 18576 1568900 0 0 0 64 215 32143 56 36 8
> 5 0 0 371612 58532 18576 1568924 0 0 0 696 363 33553 52 41 7
> 8 0 0 371612 59344 18576 1568956 0 0 16 240 374 34237 52 38 9
> 3 0 0 371612 58860 18576 1568996 0 0 0 128 254 31848 51 38 11
> 6 0 0 371612 59172 18576 1568996 0 0 0 64 234 36340 56 30 14
> 3 0 0 371612 59092 18576 1569004 0 0 0 232 204 32065 48 42 11
> ^^^^^
> Check out those figures for context switches! 30,000 switches per second
> with only three runnable processes and practically no block I/O seems
> quite high to me. You can also see that the system is spending half its
> time in the kernel, presumably in the scheduler. Postgres is barely
> getting any CPU time at all, and the performance suffers noticeably.
>
> Is this a scheduler worst-case, something to be expected, or something I
> can work around?
>
> Please CC me since vger's majordomo is an impossible chunk of shit.
>
> -jwb
>
> -
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