Re: Time sliced CFQ io scheduler

Prakash K. Cheemplavam
2004-12-02T22:16:00Z

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Andrew Morton schrieb:
> Jens Axboe <axboe@suse.de> wrote:
>
>>n Thu, Dec 02 2004, Andrew Morton wrote:
>>
>>>Jens Axboe <axboe@suse.de> wrote:
>>>
>>>>as:
>>>>Reader: 27985KiB/sec (max_lat=34msec)
>>>>Writer: 64KiB/sec (max_lat=1042msec)
>>>>
>>>>cfq:
>>>>Reader: 12703KiB/sec (max_lat=108msec)
>>>>Writer: 9743KiB/sec (max_lat=89msec)
>
>
> Did a quick test here, things seem OK.
>
> Writer:
>
> while true
> do
> dd if=/dev/zero of=foo bs=1M count=1000 conv=notrunc
> done
>
> Reader:
>
> time cat 1-gig-file > /dev/null
> cat x > /dev/null 0.07s user 1.55s system 3% cpu 45.434 total
>
> `vmstat 1' says:
>
>
> 0 5 1168 3248 472 220972 0 0 28 24896 1249 212 0 7 0 94
> 0 7 1168 3248 492 220952 0 0 28 28056 1284 204 0 5 0 96
> 0 8 1168 3248 500 221012 0 0 28 30632 1255 194 0 5 0 95
> 0 7 1168 2800 508 221344 0 0 16 20432 1183 170 0 3 0 97
> 0 8 1168 3024 484 221164 0 0 15008 12488 1246 460 0 4 0 96
> 1 8 1168 2252 484 221980 0 0 27808 6092 1270 624 0 4 0 96
> 0 8 1168 3248 468 221044 0 0 32420 4596 1290 690 0 4 0 96
> 0 9 1164 2084 456 222212 4 0 28964 1800 1285 596 0 3 0 96
> 1 7 1164 3032 392 221256 0 0 23456 6820 1270 527 0 4 0 96
> 0 9 1164 3200 388 221124 0 0 27040 7868 1269 588 0 3 0 97
> 0 9 1164 2540 384 221808 0 0 21536 4024 1247 540 0 4 0 96
> procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy id wa
> 1 10 1164 2052 392 222276 0 0 33572 5268 1298 745 0 4 0 96
> 0 9 1164 3032 400 221316 0 0 28704 5448 1282 611 0 4 0 97
>

I am happy that finally the kernel devs see that there is a problem. In my case (as I
mentioned in another thread) the reader is pretty starving while I a writer is active.
(esp my email client makes trouble while writing is going on.) This is vmstat using your
scripts above (though using cfq2 scheduler):

procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
1 3 3080 2528 1256 818976 0 0 6404 101236 1332 929 1 26 0 73
0 3 3080 2768 1252 820104 0 0 2820 32632 1328 1087 1 20 0 79
2 1 3080 6992 1292 814808 0 0 4928 106912 1337 1364 16 29 0 55
0 3 3080 2772 1252 818516 0 0 3076 42176 1357 1351 2 41 0 57
0 3 3080 2644 1256 817548 0 0 3332 110104 1375 873 1 36 0 63
0 3 3080 2592 1248 815928 0 0 2820 76860 1324 894 1 41 0 58
7 3 3080 2208 1248 817176 0 0 3328 134144 1352 1058 2 30 0 68
4 4 3080 2516 1248 817516 0 0 3588 47768 1327 1244 1 19 0 80
0 3 3080 2400 1220 818688 0 0 3844 24760 1312 1251 1 23 0 76
0 3 3080 2656 1196 816468 0 0 3588 132372 1352 1126 1 52 0 47
0 3 3080 2688 1188 815316 0 0 3076 77824 1328 933 1 35 0 64
0 3 3080 2336 1156 816744 0 0 2924 114688 1333 1038 1 25 0 74
0 3 3080 2528 1184 816812 0 0 2508 67736 1340 882 1 12 0 87
0 3 3080 2208 1156 817712 0 0 3592 75624 1326 2289 1 36 0 63
0 3 3080 2664 1156 818240 0 0 5124 15692 1302 992 1 18 0 81
0 3 3080 2580 1160 815832 0 0 4356 155792 1375 1064 1 39 0 60
0 3 3080 2472 1160 817124 0 0 3076 100852 1345 1138 1 23 0 76
2 4 3080 2836 1148 816228 0 0 3336 100412 1352 1379 1 47 0 52
0 4 3080 2708 1144 815964 0 0 3844 48908 1343 871 1 25 0 74
0 3 3080 2748 1152 815984 0 0 3332 71996 1338 843 1 27 0 72

Cheers,

Prakash

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