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author | Vivek Goyal <vgoyal@redhat.com> | 2010-12-01 18:34:46 (GMT) |
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committer | Jens Axboe <jaxboe@fusionio.com> | 2010-12-01 18:34:46 (GMT) |
commit | d1ae8ffdfaa16b2ab2e9346e81cf0ab6eaaae347 (patch) | |
tree | d34fabaf556ec4471e076b4794fa1de8515956f0 /drivers/md/dm-table.c | |
parent | 5478755616ae2ef1ce144dded589b62b2a50d575 (diff) | |
download | linux-d1ae8ffdfaa16b2ab2e9346e81cf0ab6eaaae347.tar.xz |
blk-throttle: Trim/adjust slice_end once a bio has been dispatched
o During some testing I did following and noticed throttling stops working.
- Put a very low limit on a cgroup, say 1 byte per second.
- Start some reads, this will set slice_end to a very high value.
- Change the limit to higher value say 1MB/s
- Now IO unthrottles and finishes as expected.
- Try to do the read again but IO is not limited to 1MB/s as expected.
o What is happening.
- Initially low value of limit sets slice_end to a very high value.
- During updation of limit, slice_end is not being truncated.
- Very high value of slice_end leads to keeping the existing slice
valid for a very long time and new slice does not start.
- tg_may_dispatch() is called in blk_throtle_bio(), and trim_slice()
is not called in this path. So slice_start is some old value and
practically we are able to do huge amount of IO.
o There are many ways it can be fixed. I have fixed it by trying to
adjust/cleanup slice_end in trim_slice(). Generally we extend slices if bio
is big and can't be dispatched in one slice. After dispatch of bio, readjust
the slice_end to make sure we don't end up with huge values.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'drivers/md/dm-table.c')
0 files changed, 0 insertions, 0 deletions