Re: Time sliced CFQ io scheduler

Jens Axboe
2004-12-03T07:02:13Z

On Thu, Dec 02 2004, Prakash K. Cheemplavam wrote:
> 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

This was the reverse case, though :-)

> 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

Can you try with the patch that is in the parent of this thread? The
above doesn't look that bad, although read performance could be better
of course. But try with the patch please, I'm sure it should help you
quite a lot.

--
Jens Axboe