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Message-Id: <20210125190248.49338-2-paolo.valente@linaro.org>
Date: Mon, 25 Jan 2021 20:02:43 +0100
From: Paolo Valente <paolo.valente@...aro.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
Paolo Valente <paolo.valente@...aro.org>,
Jan Kara <jack@...e.cz>
Subject: [PATCH BUGFIX/IMPROVEMENT 1/6] block, bfq: replace mechanism for evaluating I/O intensity
Some BFQ mechanisms make their decisions on a bfq_queue basing also on
whether the bfq_queue is I/O bound. In this respect, the current logic
for evaluating whether a bfq_queue is I/O bound is rather rough. This
commits replaces this logic with a more effective one.
The new logic measures the percentage of time during which a bfq_queue
is active, and marks the bfq_queue as I/O bound if the latter if this
percentage is above a fixed threshold.
Tested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
block/bfq-iosched.c | 63 +++++++++++++++++++++++++++++++--------------
block/bfq-iosched.h | 16 ++++++------
2 files changed, 52 insertions(+), 27 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index c045613ce927..db393f5d70ba 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1026,6 +1026,8 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
bfqq->entity.new_weight = bic->saved_weight;
bfqq->ttime = bic->saved_ttime;
+ bfqq->io_start_time = bic->saved_io_start_time;
+ bfqq->tot_idle_time = bic->saved_tot_idle_time;
bfqq->wr_coeff = bic->saved_wr_coeff;
bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
@@ -1721,17 +1723,6 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
bfq_clear_bfqq_just_created(bfqq);
-
- if (!bfq_bfqq_IO_bound(bfqq)) {
- if (arrived_in_time) {
- bfqq->requests_within_timer++;
- if (bfqq->requests_within_timer >=
- bfqd->bfq_requests_within_timer)
- bfq_mark_bfqq_IO_bound(bfqq);
- } else
- bfqq->requests_within_timer = 0;
- }
-
if (bfqd->low_latency) {
if (unlikely(time_is_after_jiffies(bfqq->split_time)))
/* wraparound */
@@ -1865,6 +1856,36 @@ static void bfq_reset_inject_limit(struct bfq_data *bfqd,
bfqq->decrease_time_jif = jiffies;
}
+static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
+{
+ u64 tot_io_time = now_ns - bfqq->io_start_time;
+
+ if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfqq->dispatched == 0)
+ bfqq->tot_idle_time +=
+ now_ns - bfqq->ttime.last_end_request;
+
+ if (unlikely(bfq_bfqq_just_created(bfqq)))
+ return;
+
+ /*
+ * Must be busy for at least about 80% of the time to be
+ * considered I/O bound.
+ */
+ if (bfqq->tot_idle_time * 5 > tot_io_time)
+ bfq_clear_bfqq_IO_bound(bfqq);
+ else
+ bfq_mark_bfqq_IO_bound(bfqq);
+
+ /*
+ * Keep an observation window of at most 200 ms in the past
+ * from now.
+ */
+ if (tot_io_time > 200 * NSEC_PER_MSEC) {
+ bfqq->io_start_time = now_ns - (tot_io_time>>1);
+ bfqq->tot_idle_time >>= 1;
+ }
+}
+
static void bfq_add_request(struct request *rq)
{
struct bfq_queue *bfqq = RQ_BFQQ(rq);
@@ -1872,6 +1893,7 @@ static void bfq_add_request(struct request *rq)
struct request *next_rq, *prev;
unsigned int old_wr_coeff = bfqq->wr_coeff;
bool interactive = false;
+ u64 now_ns = ktime_get_ns();
bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
bfqq->queued[rq_is_sync(rq)]++;
@@ -1934,7 +1956,7 @@ static void bfq_add_request(struct request *rq)
*/
if (bfqd->last_completed_rq_bfqq &&
!bfq_bfqq_has_short_ttime(bfqq) &&
- ktime_get_ns() - bfqd->last_completion <
+ now_ns - bfqd->last_completion <
4 * NSEC_PER_MSEC) {
if (bfqd->last_completed_rq_bfqq != bfqq &&
bfqd->last_completed_rq_bfqq !=
@@ -2051,6 +2073,9 @@ static void bfq_add_request(struct request *rq)
}
}
+ if (bfq_bfqq_sync(bfqq))
+ bfq_update_io_intensity(bfqq, now_ns);
+
elv_rb_add(&bfqq->sort_list, rq);
/*
@@ -2712,6 +2737,8 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
bic->saved_ttime = bfqq->ttime;
bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
+ bic->saved_io_start_time = bfqq->io_start_time;
+ bic->saved_tot_idle_time = bfqq->tot_idle_time;
bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
if (unlikely(bfq_bfqq_just_created(bfqq) &&
@@ -3979,10 +4006,6 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
bfq_bfqq_charge_time(bfqd, bfqq, delta);
- if (reason == BFQQE_TOO_IDLE &&
- entity->service <= 2 * entity->budget / 10)
- bfq_clear_bfqq_IO_bound(bfqq);
-
if (bfqd->low_latency && bfqq->wr_coeff == 1)
bfqq->last_wr_start_finish = jiffies;
@@ -5088,6 +5111,8 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
struct bfq_io_cq *bic, pid_t pid, int is_sync)
{
+ u64 now_ns = ktime_get_ns();
+
RB_CLEAR_NODE(&bfqq->entity.rb_node);
INIT_LIST_HEAD(&bfqq->fifo);
INIT_HLIST_NODE(&bfqq->burst_list_node);
@@ -5115,7 +5140,9 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfq_clear_bfqq_sync(bfqq);
/* set end request to minus infinity from now */
- bfqq->ttime.last_end_request = ktime_get_ns() + 1;
+ bfqq->ttime.last_end_request = now_ns + 1;
+
+ bfqq->io_start_time = now_ns;
bfq_mark_bfqq_IO_bound(bfqq);
@@ -6529,8 +6556,6 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
bfqd->bfq_slice_idle = bfq_slice_idle;
bfqd->bfq_timeout = bfq_timeout;
- bfqd->bfq_requests_within_timer = 120;
-
bfqd->bfq_large_burst_thresh = 8;
bfqd->bfq_burst_interval = msecs_to_jiffies(180);
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 703895224562..c913b06016b3 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -291,6 +291,11 @@ struct bfq_queue {
/* associated @bfq_ttime struct */
struct bfq_ttime ttime;
+ /* when bfqq started to do I/O within the last observation window */
+ u64 io_start_time;
+ /* how long bfqq has remained empty during the last observ. window */
+ u64 tot_idle_time;
+
/* bit vector: a 1 for each seeky requests in history */
u32 seek_history;
@@ -407,6 +412,9 @@ struct bfq_io_cq {
*/
bool saved_IO_bound;
+ u64 saved_io_start_time;
+ u64 saved_tot_idle_time;
+
/*
* Same purpose as the previous fields for the value of the
* field keeping the queue's belonging to a large burst
@@ -641,14 +649,6 @@ struct bfq_data {
*/
unsigned int bfq_timeout;
- /*
- * Number of consecutive requests that must be issued within
- * the idle time slice to set again idling to a queue which
- * was marked as non-I/O-bound (see the definition of the
- * IO_bound flag for further details).
- */
- unsigned int bfq_requests_within_timer;
-
/*
* Force device idling whenever needed to provide accurate
* service guarantees, without caring about throughput
--
2.20.1
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