Re: 100% iowait on one of cpus in current -git

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On 11/1/07, Torsten Kaiser <[email protected]> wrote:
> On 11/1/07, Fengguang Wu <[email protected]> wrote:
> > Thank you. Maybe we can start by the applied debug patch :-)
>
> Will applied it and try to recreate this.

Patch applied, used emerge to install a 2.6.24-rc1 kernel.

I had no complete stalls, but three times during the move from tmpfs
to the main xfs the emerge got noticeable slower. There still was
writeout happening, but as emerge prints out every file it has written
during the pause not one file was processed.

vmstat 10:
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  1      0 3146424    332 614768    0    0   134  1849  438 2515  3  4 91  2
 0  0      0 3146644    332 614784    0    0     2  1628  507  646  0  2 85 13
 0  0      0 3146868    332 614868    0    0     5  2359  527 1076  0  3 97  0
 1  0      0 3144372    332 616148    0    0    96  2829  607 2666  2  5 92  0
-> normal writeout
 0  0      0 3140560    332 618144    0    0   152  2764  633 3308  3  6 91  0
 0  0      0 3137332    332 619908    0    0   114  1801  588 2858  3  4 93  0
 0  0      0 3136912    332 620136    0    0    20   827  393 1605  1  2 98  0
-> first stall
 0  0      0 3137088    332 620136    0    0     0   557  339 1437  0  1 99  0
 0  0      0 3137160    332 620136    0    0     0   642  310 1400  0  1 99  0
 0  0      0 3136588    332 620172    0    0     6  2972  527 1195  0  3 80 16
 0  0      0 3136276    332 620348    0    0    10  2668  558 1195  0  3 96  0
 0  0      0 3135228    332 620424    0    0     8  2712  522 1311  0  4 96  0
 0  0      0 3131740    332 621524    0    0    75  2935  559 2457  2  5 93  0
 0  0      0 3128348    332 622972    0    0    85  1470  490 2607  3  4 93  0
 0  0      0 3129292    332 622972    0    0     0   527  353 1398  0  1 99  0
-> second longer stall
 0  0      0 3128520    332 623028    0    0     6   488  249 1390  0  1 99  0
 0  0      0 3128236    332 623028    0    0     0   482  222 1222  0  1 99  0
 0  0      0 3128408    332 623028    0    0     0   585  269 1301  0  0 99  0
 0  0      0 3128532    332 623028    0    0     0   610  262 1278  0  0 99  0
 0  0      0 3128568    332 623028    0    0     0   636  345 1639  0  1 99  0
 0  0      0 3129032    332 623040    0    0     1   664  337 1466  0  1 99  0
 0  0      0 3129484    332 623040    0    0     0   658  300 1508  0  0 100  0
 0  0      0 3129576    332 623040    0    0     0   562  271 1454  0  1 99  0
 0  0      0 3129736    332 623040    0    0     0   627  278 1406  0  1 99  0
 0  0      0 3129368    332 623040    0    0     0   507  274 1301  0  1 99  0
 0  0      0 3129004    332 623040    0    0     0   444  211 1213  0  0 99  0
 0  1      0 3127260    332 623040    0    0     0  1036  305 1242  0  1 95  4
 0  0      0 3126280    332 623128    0    0     7  4241  555 1575  1  5 84 10
 0  0      0 3124948    332 623232    0    0     6  4194  529 1505  1  4 95  0
 0  0      0 3125228    332 624168    0    0    58  1966  586 1964  2  4 94  0
-> emerge resumed to normal speed, without any intervention from my side
 0  0      0 3120932    332 625904    0    0   112  1546  546 2565  3  4 93  0
 0  0      0 3118012    332 627568    0    0   128  1542  612 2705  3  4 93  0


>From syslog:
first stall:
[  575.050000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 47259
global 610 0 0 wc __ tw 1023 sk 0
[  586.350000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 50465
global 6117 0 0 wc _M tw 967 sk 0
[  586.360000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 50408
global 6117 0 0 wc __ tw 1022 sk 0
[  599.900000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 53523
global 11141 0 0 wc __ tw 1009 sk 0
[  635.780000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 59397
global 12757 124 0 wc __ tw 0 sk 0
[  638.470000] mm/page-writeback.c 418 balance_dirty_pages:
emerge(6113) 1536 global 11405 51 0 wc __ tw 0 sk 0
[  638.820000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 58373
global 11276 48 0 wc __ tw -1 sk 0
[  641.260000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 57348
global 10565 100 0 wc __ tw 0 sk 0
[  643.980000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 56324
global 9788 103 0 wc __ tw -1 sk 0
[  646.120000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 55299
global 8912 6 0 wc __ tw 0 sk 0

second stall:
[  664.040000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 48117
global 2864 81 0 wc _M tw -13 sk 0
[  664.400000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 47080
global 1995 137 0 wc _M tw 176 sk 0
[  664.510000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 46232
global 1929 267 0 wc __ tw 880 sk 0
cron[6927]: (root) CMD (test -x /usr/sbin/run-crons && /usr/sbin/run-crons )
[  809.560000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 49422
global 19166 217 0 wc _M tw 380 sk 0
[  811.720000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 48778
global 17969 407 0 wc _M tw -4 sk 0
[  813.880000] mm/page-writeback.c 418 balance_dirty_pages:
emerge(6113) 1537 global 16592 233 0 wc _M tw -1 sk 0
[  814.710000] mm/page-writeback.c 418 balance_dirty_pages: find(6931)
1537 global 16132 179 0 wc __ tw -1 sk 0
[  814.720000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 47750
global 16040 271 0 wc _M tw -1 sk 0
[  815.040000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 46725
global 15403 779 0 wc CM tw 324 sk 0

the third stall happend after the emerge was finished. There still was
~120Mb of dirty data, but its writeout got much slower over several
seconds.
vmstat 10:
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 1  0      0 3096152    332 630424    0    0    81  1503  640 2771  5  4 91  0
 0  0      0 3101024    332 631588    0    0   279   473  510 1281  5  2 92  1
-> stall / slowdown starts
 0  0      0 3147924    332 632384    0    0    78   626  449 1384  0  1 99  0
 1  0      0 3147940    332 632384    0    0     0   611  388 1387  0  1 99  0
 0  1      0 3147576    332 632384    0    0     0   939  449 1432  0  1 99  0
 0  0      0 3145476    332 632384    0    0     0  3592  644  925  0  4 93  3
-> writeout resumes full speed
 0  0      0 3147232    332 632480    0    0     0  3108  678 1053  0  3 97  0
 0  0      0 3146860    332 632480    0    0     0  2497  677  859  0  3 97  0
 0  0      0 3146720    332 632480    0    0     0  2433  648  839  0  3 97  0
 0  0      0 3147844    332 632484    0    0     0  2394  625  889  0  3 97  0
 0  0      0 3148128    332 632484    0    0     0  2204  671  848  0  2 97  0

from syslog:
[  848.070000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 48084
global 13805 0 0 wc _M tw 1008 sk 0
[  848.080000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 48068
global 13805 0 0 wc __ tw 1020 sk 0
[  884.090000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 61811
global 30297 2 0 wc __ tw 862 sk 0
[  921.760000] mm/page-writeback.c 418 balance_dirty_pages: cat(7170)
1541 global 28113 391 0 wc __ tw -5 sk 0
-> that cat was probably my watch cat /proc/meminfo
-> during the stall there where no updates visible there
[  922.190000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 76871
global 27735 0 0 wc __ tw -5 sk 0
[  923.550000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 75842
global 26688 106 0 wc _M tw -1 sk 0
[  924.940000] mm/page-writeback.c 655 wb_kupdate: pdflush(285) 74817
global 25698 195 0 wc _M tw 0 sk 0

Apart from my normal kde desktop (no compiz) and the emerge the system was idle.

If I see the complete stall again, I will post that too.

Torsten
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