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SubjectRe: 2.5.32 IO performance issues
Date
> 
> Badari Pulavarty wrote:
> >
> > Hi,
> >
> > I am having severe IO performance problems with 2.5.32 (2.5.31 works fine).
> > I was wondering what caused this.
> >
> > As you can see, IO rate went from
> >
> > 384MB/sec with 6% CPU utilization on 2.5.31
> > to
> > 120MB/sec with 19% CPU utilization on 2.5.32
> >
> > ...
> > 151712 default_idle 2370.5000
> > 21622 __scsi_end_request 122.8523
>
> block-highmem is bust for scsi. (aic7xxx at least). Does
> http://www.zip.com.au/~akpm/linux/patches/2.5/2.5.32/2.5.32-mm2/broken-out/scsi_hack.patch
> fix it?

Hmm !! This patch fixed it. I remember you gave me this patch for 2.5.31. But 2.5.31
was doing fine without it. But 2.5.32 seem to need it.

procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
1 38 0 0 3811160 0 23532 0 0 384461 0 3981 6346 0 5 95
0 39 0 0 3811152 0 23532 0 0 384499 0 3967 6354 0 5 95
0 39 0 0 3811148 0 23532 0 0 384154 0 3974 6341 0 5 95
0 39 0 0 3811144 0 23532 0 0 384013 0 3964 6344 0 5 95
0 39 0 0 3811204 0 23532 0 0 384154 0 3966 6357 0 5 95
0 39 0 0 3811176 0 23532 0 0 384256 0 3973 6341 0 5 95
0 39 0 0 3811168 0 23532 0 0 384320 0 3969 6329 0 5 95
0 39 0 0 3811152 0 23532 0 0 384294 0 3980 6335 0 5 95

Here is the profile output with this patch:

# readprofile | sort -nr +2
221145 default_idle 3455.3906
3163 do_softirq 16.4740
1489 __scsi_end_request 8.4602
1696 scsi_dispatch_cmd 2.7895
371 dio_bio_complete 2.1080
509 blk_rq_map_sg 1.3255
198 dio_await_one 1.2375
57 dio_prep_bio 1.1875
56 bio_put 1.1667
71 __generic_copy_to_user 1.1094
630 do_direct_IO 0.9157
42 __wake_up 0.8750
297 __set_page_dirty_buffers 0.8438
622 schedule 0.6942
629 __make_request 0.5460
402 get_user_pages 0.5346
17 scsi_sense_valid 0.5312
42 bio_destructor 0.5250
198 bio_alloc 0.4760
32 dio_get_page 0.4000

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