md/raid1: Use a new variable to count flighting sync requests

In new barrier codes, raise_barrier waits if conf->nr_pending[idx] is not zero.
After all the conditions are true, the resync request can go on be handled. But
it adds conf->nr_pending[idx] again. The next resync request hit the same bucket
idx need to wait the resync request which is submitted before. The performance
of resync/recovery is degraded.
So we should use a new variable to count sync requests which are in flight.

I did a simple test:
1. Without the patch, create a raid1 with two disks. The resync speed:
Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
sdb               0.00     0.00  166.00    0.00    10.38     0.00   128.00     0.03    0.20    0.20    0.00   0.19   3.20
sdc               0.00     0.00    0.00  166.00     0.00    10.38   128.00     0.96    5.77    0.00    5.77   5.75  95.50
2. With the patch, the result is:
sdb            2214.00     0.00  766.00    0.00   185.69     0.00   496.46     2.80    3.66    3.66    0.00   1.03  79.10
sdc               0.00  2205.00    0.00  769.00     0.00   186.44   496.52     5.25    6.84    0.00    6.84   1.30 100.10

Suggested-by: Shaohua Li <shli@kernel.org>
Signed-off-by: Xiao Ni <xni@redhat.com>
Acked-by: Coly Li <colyli@suse.de>
Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 70a596c10306aacda32526e62a57cdc6bfc50003..5d19c1a7d90a813d4d956ba1b48a161efbb186a7 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -885,7 +885,7 @@ static void raise_barrier(struct r1conf *conf, sector_t sector_nr)
                             atomic_read(&conf->barrier[idx]) < RESYNC_DEPTH,
                            conf->resync_lock);
 
-       atomic_inc(&conf->nr_pending[idx]);
+       atomic_inc(&conf->nr_sync_pending);
        spin_unlock_irq(&conf->resync_lock);
 }
 
@@ -896,7 +896,7 @@ static void lower_barrier(struct r1conf *conf, sector_t sector_nr)
        BUG_ON(atomic_read(&conf->barrier[idx]) <= 0);
 
        atomic_dec(&conf->barrier[idx]);
-       atomic_dec(&conf->nr_pending[idx]);
+       atomic_dec(&conf->nr_sync_pending);
        wake_up(&conf->wait_barrier);
 }
 
@@ -1033,7 +1033,8 @@ static int get_unqueued_pending(struct r1conf *conf)
 {
        int idx, ret;
 
-       for (ret = 0, idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
+       ret = atomic_read(&conf->nr_sync_pending);
+       for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
                ret += atomic_read(&conf->nr_pending[idx]) -
                        atomic_read(&conf->nr_queued[idx]);
 

diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index b0ab0da6e39ef37a1ac9c4954fddd2c90185d47c..c8894ef1e9d25d4cf7cb0561793bda9c7365a647 100644 (file)
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -84,6 +84,7 @@ struct r1conf {
         */
        wait_queue_head_t       wait_barrier;
        spinlock_t              resync_lock;
+       atomic_t                nr_sync_pending;
        atomic_t                *nr_pending;
        atomic_t                *nr_waiting;
        atomic_t                *nr_queued;