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author | Vivek Goyal <vgoyal@redhat.com> | 2010-12-01 19:34:46 +0100 |
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committer | Jens Axboe <jaxboe@fusionio.com> | 2010-12-01 19:34:46 +0100 |
commit | d1ae8ffdfaa16b2ab2e9346e81cf0ab6eaaae347 (patch) | |
tree | d34fabaf556ec4471e076b4794fa1de8515956f0 /block | |
parent | 5478755616ae2ef1ce144dded589b62b2a50d575 (diff) | |
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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 'block')
-rw-r--r-- | block/blk-throttle.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 004be80..2d134b7 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -355,6 +355,12 @@ throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw) tg->slice_end[rw], jiffies); } +static inline void throtl_set_slice_end(struct throtl_data *td, + struct throtl_grp *tg, bool rw, unsigned long jiffy_end) +{ + tg->slice_end[rw] = roundup(jiffy_end, throtl_slice); +} + static inline void throtl_extend_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw, unsigned long jiffy_end) { @@ -391,6 +397,16 @@ throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw) if (throtl_slice_used(td, tg, rw)) return; + /* + * A bio has been dispatched. Also adjust slice_end. It might happen + * that initially cgroup limit was very low resulting in high + * slice_end, but later limit was bumped up and bio was dispached + * sooner, then we need to reduce slice_end. A high bogus slice_end + * is bad because it does not allow new slice to start. + */ + + throtl_set_slice_end(td, tg, rw, jiffies + throtl_slice); + time_elapsed = jiffies - tg->slice_start[rw]; nr_slices = time_elapsed / throtl_slice; |