raid5: make_request does less prepare wait

In NUMA machine, prepare_to_wait/finish_wait in make_request exposes a
lot of contention for sequential workload (or big request size
workload). For such workload, each bio includes several stripes. So we
can just do prepare_to_wait/finish_wait once for the whold bio instead
of every stripe.  This reduces the lock contention completely for such
workload. Random workload might have the similar lock contention too,
but I didn't see it yet, maybe because my stroage is still not fast
enough.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 14 insertions, 5 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 16f5c21963db..a904a2c80fc8 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4552,6 +4552,8 @@ static void make_request(struct mddev *mddev, struct bio * bi)
         struct stripe_head *sh;
         const int rw = bio_data_dir(bi);
         int remaining;
+        DEFINE_WAIT(w);
+        bool do_prepare;
 
         if (unlikely(bi->bi_rw & REQ_FLUSH)) {
                 md_flush_request(mddev, bi);
@@ -4575,15 +4577,18 @@ static void make_request(struct mddev *mddev, struct bio * bi)
         bi->bi_next = NULL;
         bi->bi_phys_segments = 1;       /* over-loaded to count active stripes */
 
+        prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
         for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
-                DEFINE_WAIT(w);
                 int previous;
                 int seq;
 
+                do_prepare = false;
         retry:
                 seq = read_seqcount_begin(&conf->gen_lock);
                 previous = 0;
-                prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
+                if (do_prepare)
+                        prepare_to_wait(&conf->wait_for_overlap, &w,
+                                TASK_UNINTERRUPTIBLE);
                 if (unlikely(conf->reshape_progress != MaxSector)) {
                         /* spinlock is needed as reshape_progress may be
                          * 64bit on a 32bit platform, and so it might be
@@ -4604,6 +4609,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                                     : logical_sector >= conf->reshape_safe) {
                                         spin_unlock_irq(&conf->device_lock);
                                         schedule();
+                                        do_prepare = true;
                                         goto retry;
                                 }
                         }
@@ -4640,6 +4646,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                                 if (must_retry) {
                                         release_stripe(sh);
                                         schedule();
+                                        do_prepare = true;
                                         goto retry;
                                 }
                         }
@@ -4663,8 +4670,10 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                                 prepare_to_wait(&conf->wait_for_overlap,
                                                 &w, TASK_INTERRUPTIBLE);
                                 if (logical_sector >= mddev->suspend_lo &&
-                                    logical_sector < mddev->suspend_hi)
+                                    logical_sector < mddev->suspend_hi) {
                                         schedule();
+                                        do_prepare = true;
+                                }
                                 goto retry;
                         }
 
@@ -4677,9 +4686,9 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                                 md_wakeup_thread(mddev->thread);
                                 release_stripe(sh);
                                 schedule();
+                                do_prepare = true;
                                 goto retry;
                         }
-                        finish_wait(&conf->wait_for_overlap, &w);
                         set_bit(STRIPE_HANDLE, &sh->state);
                         clear_bit(STRIPE_DELAYED, &sh->state);
                         if ((bi->bi_rw & REQ_SYNC) &&
@@ -4689,10 +4698,10 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                 } else {
                         /* cannot get stripe for read-ahead, just give-up */
                         clear_bit(BIO_UPTODATE, &bi->bi_flags);
-                        finish_wait(&conf->wait_for_overlap, &w);
                         break;
                 }
         }
+        finish_wait(&conf->wait_for_overlap, &w);
 
         remaining = raid5_dec_bi_active_stripes(bi);
         if (remaining == 0) {