Re: Time sliced CFQ io scheduler

[Jens Axboe <axboe@suse.de>]

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