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blkio: Recalculate the throttled bio dispatch time upon throttle limit change

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o Currently any cgroup throttle limit changes are processed asynchronousy and
  the change does not take affect till a new bio is dispatched from same group.

o It might happen that a user sets a redicuously low limit on throttling.
  Say 1 bytes per second on reads. In such cases simple operations like mount
  a disk can wait for a very long time.

o Once bio is throttled, there is no easy way to come out of that wait even if
  user increases the read limit later.

o This patch fixes it. Now if a user changes the cgroup limits, we recalculate
  the bio dispatch time according to new limits.

o Can't take queueu lock under blkcg_lock, hence after the change I wake
  up the dispatch thread again which recalculates the time. So there are some
  variables being synchronized across two threads without lock and I had to
  make use of barriers. Hoping I have used barriers correctly. Any review of
  memory barrier code especially will help.

Signed-off-by: Vivek Goyal <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Vivek Goyal 2010-10-01 14:49:49 +02:00 • committed by Jens Axboe
commit fe0714377e
4 changed files with 139 additions and 35 deletions
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4
block/cfq-iosched.c
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@ -951,8 +951,8 @@ static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
return NULL;
}
void
cfq_update_blkio_group_weight(struct blkio_group *blkg, unsigned int weight)
void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
unsigned int weight)
{
cfqg_of_blkg(blkg)->weight = weight;
}