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authorJens Axboe <axboe@fb.com>2014-04-16 11:36:54 -0600
committerJens Axboe <axboe@fb.com>2014-04-16 14:15:25 -0600
commitf793aa53786668c9e0db5900f70f560e99d62fa0 (patch)
tree312275021f0186a58a328ff0882f03bf0cb36e1a
parent12120077b2612a243d158605640cd39266906667 (diff)
block: relax when to modify the timeout timer
Since we are now, by default, applying timer slack to expiry times, the logic for when to modify a timer in the block code is suboptimal. The block layer keeps a forward rolling timer per queue for all requests, and modifies this timer if a request has a shorter timeout than what the current expiry time is. However, this breaks down when our rounded timer values get applied slack. Then each new request ends up modifying the timer, since we're still a little in front of the timer + slack. Fix this by allowing a tolerance of HZ / 2, the timeout handling doesn't need to be very precise. This drastically cuts down the number of timer modifications we have to make. Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--block/blk-timeout.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index d96f7061c6fd..a09e8af8186c 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -199,8 +199,19 @@ void __blk_add_timer(struct request *req, struct list_head *timeout_list)
expiry = round_jiffies_up(req->deadline);
if (!timer_pending(&q->timeout) ||
- time_before(expiry, q->timeout.expires))
- mod_timer(&q->timeout, expiry);
+ time_before(expiry, q->timeout.expires)) {
+ unsigned long diff = q->timeout.expires - expiry;
+
+ /*
+ * Due to added timer slack to group timers, the timer
+ * will often be a little in front of what we asked for.
+ * So apply some tolerance here too, otherwise we keep
+ * modifying the timer because expires for value X
+ * will be X + something.
+ */
+ if (diff >= HZ / 2)
+ mod_timer(&q->timeout, expiry);
+ }
}