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authorDavide Sapienza <sapienza.dav@gmail.com>2018-05-31 16:45:08 +0200
committerJens Axboe <axboe@kernel.dk>2018-05-31 08:54:41 -0600
commitf6c3ca0e58446e8de6c6f1a2a73f037fb900c372 (patch)
tree4bb57aa40714ad8cdeff7eebe0ecd26a08d13662 /block/bfq-iosched.c
parentd450542e3ce0efd030316b7846cc7231300b2bc9 (diff)
downloadlinux-0-day-f6c3ca0e58446e8de6c6f1a2a73f037fb900c372.tar.gz
block, bfq: prevent soft_rt_next_start from being stuck at infinity
BFQ can deem a bfq_queue as soft real-time only if the queue - periodically becomes completely idle, i.e., empty and with no still-outstanding I/O request; - after becoming idle, gets new I/O only after a special reference time soft_rt_next_start. In this respect, after commit "block, bfq: consider also past I/O in soft real-time detection", the value of soft_rt_next_start can never decrease. This causes a problem with the following special updating case for soft_rt_next_start: to prevent queues that are not completely idle to be wrongly detected as soft real-time (when they become non-empty again), soft_rt_next_start is temporarily set to infinity for empty queues with still outstanding I/O requests. But, if such an update is actually performed, then, because of the above commit, soft_rt_next_start will be stuck at infinity forever, and the queue will have no more chance to be considered soft real-time. On slow systems, this problem does cause actual soft real-time applications to be occasionally not detected as such. This commit addresses this issue by eliminating the pushing of soft_rt_next_start to infinity, and by changing the way non-empty queues are prevented from being wrongly detected as soft real-time. Simply, a queue that becomes non-empty again can now be detected as soft real-time only if it has no outstanding I/O request. Signed-off-by: Davide Sapienza <sapienza.dav@gmail.com> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bfq-iosched.c')
-rw-r--r--block/bfq-iosched.c29
1 files changed, 2 insertions, 27 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 128b3be..495b9dd 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1363,15 +1363,6 @@ static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
}
/*
- * Return the farthest future time instant according to jiffies
- * macros.
- */
-static unsigned long bfq_greatest_from_now(void)
-{
- return jiffies + MAX_JIFFY_OFFSET;
-}
-
-/*
* Return the farthest past time instant according to jiffies
* macros.
*/
@@ -1515,7 +1506,8 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
in_burst = bfq_bfqq_in_large_burst(bfqq);
soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
!in_burst &&
- time_is_before_jiffies(bfqq->soft_rt_next_start);
+ time_is_before_jiffies(bfqq->soft_rt_next_start) &&
+ bfqq->dispatched == 0;
*interactive = !in_burst && idle_for_long_time;
wr_or_deserves_wr = bfqd->low_latency &&
(bfqq->wr_coeff > 1 ||
@@ -3222,23 +3214,6 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
bfq_bfqq_softrt_next_start(bfqd, bfqq);
else {
/*
- * The application is still waiting for the
- * completion of one or more requests:
- * prevent it from possibly being incorrectly
- * deemed as soft real-time by setting its
- * soft_rt_next_start to infinity. In fact,
- * without this assignment, the application
- * would be incorrectly deemed as soft
- * real-time if:
- * 1) it issued a new request before the
- * completion of all its in-flight
- * requests, and
- * 2) at that time, its soft_rt_next_start
- * happened to be in the past.
- */
- bfqq->soft_rt_next_start =
- bfq_greatest_from_now();
- /*
* Schedule an update of soft_rt_next_start to when
* the task may be discovered to be isochronous.
*/