block: consolidate struct request timestamp fields

Currently, struct request has four timestamp fields:

- A start time, set at get_request time, in jiffies, used for iostats
- An I/O start time, set at start_request time, in ktime nanoseconds,
  used for blk-stats (i.e., wbt, kyber, hybrid polling)
- Another start time and another I/O start time, used for cfq and bfq

These can all be consolidated into one start time and one I/O start
time, both in ktime nanoseconds, shaving off up to 16 bytes from struct
request depending on the kernel config.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

8 files changed, 27 insertions, 39 deletions

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 771ae9730ac6..ebc264c87a09 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4778,8 +4778,8 @@ static void bfq_finish_requeue_request(struct request *rq)
 
         if (rq->rq_flags & RQF_STARTED)
                 bfqg_stats_update_completion(bfqq_group(bfqq),
-                                             rq_start_time_ns(rq),
-                                             rq_io_start_time_ns(rq),
+                                             rq->start_time_ns,
+                                             rq->io_start_time_ns,
                                              rq->cmd_flags);
 
         if (likely(rq->rq_flags & RQF_STARTED)) {
diff --git a/block/blk-core.c b/block/blk-core.c
index 33d5c7d85da1..1418a1ccd80d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -196,8 +196,7 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
         RB_CLEAR_NODE(&rq->rb_node);
         rq->tag = -1;
         rq->internal_tag = -1;
-        rq->start_time = jiffies;
-        set_start_time_ns(rq);
+        rq->start_time_ns = ktime_get_ns();
         rq->part = NULL;
         seqcount_init(&rq->gstate_seq);
         u64_stats_init(&rq->aborted_gstate_sync);
@@ -2726,7 +2725,7 @@ void blk_account_io_completion(struct request *req, unsigned int bytes)
         }
 }
 
-void blk_account_io_done(struct request *req)
+void blk_account_io_done(struct request *req, u64 now)
 {
         /*
          * Account IO completion.  flush_rq isn't accounted as a
@@ -2734,11 +2733,12 @@ void blk_account_io_done(struct request *req)
          * containing request is enough.
          */
         if (blk_do_io_stat(req) && !(req->rq_flags & RQF_FLUSH_SEQ)) {
-                unsigned long duration = jiffies - req->start_time;
+                unsigned long duration;
                 const int rw = rq_data_dir(req);
                 struct hd_struct *part;
                 int cpu;
 
+                duration = nsecs_to_jiffies(now - req->start_time_ns);
                 cpu = part_stat_lock();
                 part = req->part;
 
@@ -2969,10 +2969,8 @@ static void blk_dequeue_request(struct request *rq)
          * and to it is freed is accounted as io that is in progress at
          * the driver side.
          */
-        if (blk_account_rq(rq)) {
+        if (blk_account_rq(rq))
                 q->in_flight[rq_is_sync(rq)]++;
-                set_io_start_time_ns(rq);
-        }
 }
 
 /**
@@ -3192,12 +3190,13 @@ EXPORT_SYMBOL_GPL(blk_unprep_request);
 void blk_finish_request(struct request *req, blk_status_t error)
 {
         struct request_queue *q = req->q;
+        u64 now = ktime_get_ns();
 
         lockdep_assert_held(req->q->queue_lock);
         WARN_ON_ONCE(q->mq_ops);
 
         if (req->rq_flags & RQF_STATS)
-                blk_stat_add(req);
+                blk_stat_add(req, now);
 
         if (req->rq_flags & RQF_QUEUED)
                 blk_queue_end_tag(q, req);
@@ -3212,7 +3211,7 @@ void blk_finish_request(struct request *req, blk_status_t error)
         if (req->rq_flags & RQF_DONTPREP)
                 blk_unprep_request(req);
 
-        blk_account_io_done(req);
+        blk_account_io_done(req, now);
 
         if (req->end_io) {
                 wbt_done(req->q->rq_wb, req);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 782940c65d8a..5573d0fbec53 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -724,13 +724,12 @@ static struct request *attempt_merge(struct request_queue *q,
         }
 
         /*
-         * At this point we have either done a back merge
-         * or front merge. We need the smaller start_time of
-         * the merged requests to be the current request
-         * for accounting purposes.
+         * At this point we have either done a back merge or front merge. We
+         * need the smaller start_time_ns of the merged requests to be the
+         * current request for accounting purposes.
          */
-        if (time_after(req->start_time, next->start_time))
-                req->start_time = next->start_time;
+        if (next->start_time_ns < req->start_time_ns)
+                req->start_time_ns = next->start_time_ns;
 
         req->biotail->bi_next = next->bio;
         req->biotail = next->biotail;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 39b4e9834d82..4e9d83594cca 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -309,7 +309,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
         RB_CLEAR_NODE(&rq->rb_node);
         rq->rq_disk = NULL;
         rq->part = NULL;
-        rq->start_time = jiffies;
+        rq->start_time_ns = ktime_get_ns();
         rq->io_start_time_ns = 0;
         rq->nr_phys_segments = 0;
 #if defined(CONFIG_BLK_DEV_INTEGRITY)
@@ -329,8 +329,6 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 
 #ifdef CONFIG_BLK_CGROUP
         rq->rl = NULL;
-        set_start_time_ns(rq);
-        rq->cgroup_io_start_time_ns = 0;
 #endif
 
         data->ctx->rq_dispatched[op_is_sync(op)]++;
@@ -506,12 +504,14 @@ EXPORT_SYMBOL_GPL(blk_mq_free_request);
 
 inline void __blk_mq_end_request(struct request *rq, blk_status_t error)
 {
+        u64 now = ktime_get_ns();
+
         if (rq->rq_flags & RQF_STATS) {
                 blk_mq_poll_stats_start(rq->q);
-                blk_stat_add(rq);
+                blk_stat_add(rq, now);
         }
 
-        blk_account_io_done(rq);
+        blk_account_io_done(rq, now);
 
         if (rq->end_io) {
                 wbt_done(rq->q->rq_wb, rq);
diff --git a/block/blk-stat.c b/block/blk-stat.c
index 725a881723b0..175c143ac5b9 100644
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -47,15 +47,14 @@ static void __blk_stat_add(struct blk_rq_stat *stat, u64 value)
         stat->nr_samples++;
 }
 
-void blk_stat_add(struct request *rq)
+void blk_stat_add(struct request *rq, u64 now)
 {
         struct request_queue *q = rq->q;
         struct blk_stat_callback *cb;
         struct blk_rq_stat *stat;
         int bucket;
-        u64 now, value;
+        u64 value;
 
-        now = ktime_get_ns();
         value = (now >= rq->io_start_time_ns) ? now - rq->io_start_time_ns : 0;
 
         blk_throtl_stat_add(rq, value);
diff --git a/block/blk-stat.h b/block/blk-stat.h
index 17c812db0aca..78399cdde9c9 100644
--- a/block/blk-stat.h
+++ b/block/blk-stat.h
@@ -65,7 +65,7 @@ struct blk_stat_callback {
 struct blk_queue_stats *blk_alloc_queue_stats(void);
 void blk_free_queue_stats(struct blk_queue_stats *);
 
-void blk_stat_add(struct request *);
+void blk_stat_add(struct request *rq, u64 now);
 
 /* record time/size info in request but not add a callback */
 void blk_stat_enable_accounting(struct request_queue *q);
diff --git a/block/blk.h b/block/blk.h
index b034fd2460c4..eaf1a8e87d11 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -186,7 +186,7 @@ unsigned int blk_plug_queued_count(struct request_queue *q);
 
 void blk_account_io_start(struct request *req, bool new_io);
 void blk_account_io_completion(struct request *req, unsigned int bytes);
-void blk_account_io_done(struct request *req);
+void blk_account_io_done(struct request *req, u64 now);
 
 /*
  * EH timer and IO completion will both attempt to 'grab' the request, make
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 652ca064de20..6b9f6b1cd33b 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -4228,8 +4228,8 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
         cfqd->rq_in_driver--;
         cfqq->dispatched--;
         (RQ_CFQG(rq))->dispatched--;
-        cfqg_stats_update_completion(cfqq->cfqg, rq_start_time_ns(rq),
-                                     rq_io_start_time_ns(rq), rq->cmd_flags);
+        cfqg_stats_update_completion(cfqq->cfqg, rq->start_time_ns,
+                                     rq->io_start_time_ns, rq->cmd_flags);
 
         cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]--;
 
@@ -4245,16 +4245,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
                                         cfqq_type(cfqq));
 
                 st->ttime.last_end_request = now;
-                /*
-                 * We have to do this check in jiffies since start_time is in
-                 * jiffies and it is not trivial to convert to ns. If
-                 * cfq_fifo_expire[1] ever comes close to 1 jiffie, this test
-                 * will become problematic but so far we are fine (the default
-                 * is 128 ms).
-                 */
-                if (!time_after(rq->start_time +
-                                  nsecs_to_jiffies(cfqd->cfq_fifo_expire[1]),
-                                jiffies))
+                if (rq->start_time_ns + cfqd->cfq_fifo_expire[1] <= now)
                         cfqd->last_delayed_sync = now;
         }