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block, bfq: update base request service times when possible 

I/O injection gets reduced if it increases the request service times
of the victim queue beyond a certain threshold.  The threshold, in its
turn, is computed as a function of the base service time enjoyed by
the queue when it undergoes no injection.

As a consequence, for injection to work properly, the above base value
has to be accurate. In this respect, such a value may vary over
time. For example, it varies if the size or the spatial locality of
the I/O requests in the queue change. It is then important to update
this value whenever possible. This commit performs this update.

Reported-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Tested-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Paolo Valente 2019-06-25 07:12:45 +02:00 committed by Jens Axboe
parent db599f9ed9
commit 24792ad01c
1 changed files with 12 additions and 1 deletions
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13
block/bfq-iosched.c
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@ -5496,7 +5496,18 @@ static void bfq_update_inject_limit(struct bfq_data *bfqd,
* start trying injection.
*/
bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
}
} else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1)
/*
* No I/O injected and no request still in service in
* the drive: these are the exact conditions for
* computing the base value of the total service time
* for bfqq. So let's update this value, because it is
* rather variable. For example, it varies if the size
* or the spatial locality of the I/O requests in bfqq
* change.
*/
bfqq->last_serv_time_ns = tot_time_ns;
/* update complete, not waiting for any request completion any longer */
bfqd->waited_rq = NULL;