Illumos 5176 - lock contention on godfather zio

5176 lock contention on godfather zio
Reviewed by: Adam Leventhal <[email protected]>
Reviewed by: Alex Reece <[email protected]>
Reviewed by: Christopher Siden <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Richard Elling <[email protected]>
Reviewed by: Bayard Bell <[email protected]>
Approved by: Garrett D'Amore <[email protected]>

References:
  https://www.illumos.org/issues/5176
  https://github.com/illumos/illumos-gate/commit/6f834bc

Porting notes:

Under Linux max_ncpus is defined as num_possible_cpus().  This is
largest number of cpu ids which might be available during the life
time of the system boot.  This value can be larger than the number
of present cpus if CONFIG_HOTPLUG_CPU is defined.

Ported by: Turbo Fredriksson <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2711

2 files changed, 20 insertions, 8 deletions

diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index d96bda3fa..1b1bf7a5c 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -1252,7 +1252,9 @@ spa_unload(spa_t *spa)
 	 * Wait for any outstanding async I/O to complete.
 	 */
 	if (spa->spa_async_zio_root != NULL) {
-		(void) zio_wait(spa->spa_async_zio_root);
+		for (i = 0; i < max_ncpus; i++)
+			(void) zio_wait(spa->spa_async_zio_root[i]);
+		kmem_free(spa->spa_async_zio_root, max_ncpus * sizeof (void *));
 		spa->spa_async_zio_root = NULL;
 	}
 
@@ -2165,7 +2167,7 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 	uberblock_t *ub = &spa->spa_uberblock;
 	uint64_t children, config_cache_txg = spa->spa_config_txg;
 	int orig_mode = spa->spa_mode;
-	int parse;
+	int parse, i;
 	uint64_t obj;
 	boolean_t missing_feat_write = B_FALSE;
 
@@ -2189,8 +2191,13 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 	/*
 	 * Create "The Godfather" zio to hold all async IOs
 	 */
-	spa->spa_async_zio_root = zio_root(spa, NULL, NULL,
-	    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_GODFATHER);
+	spa->spa_async_zio_root = kmem_alloc(max_ncpus * sizeof (void *),
+	    KM_SLEEP);
+	for (i = 0; i < max_ncpus; i++) {
+		spa->spa_async_zio_root[i] = zio_root(spa, NULL, NULL,
+		    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
+		    ZIO_FLAG_GODFATHER);
+	}
 
 	/*
 	 * Parse the configuration into a vdev tree.  We explicitly set the
@@ -3495,7 +3502,7 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 	uint64_t version, obj;
 	boolean_t has_features;
 	nvpair_t *elem;
-	int c;
+	int c, i;
 	char *poolname;
 	nvlist_t *nvl;
 
@@ -3556,8 +3563,13 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 	/*
 	 * Create "The Godfather" zio to hold all async IOs
 	 */
-	spa->spa_async_zio_root = zio_root(spa, NULL, NULL,
-	    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_GODFATHER);
+	spa->spa_async_zio_root = kmem_alloc(max_ncpus * sizeof (void *),
+	    KM_SLEEP);
+	for (i = 0; i < max_ncpus; i++) {
+		spa->spa_async_zio_root[i] = zio_root(spa, NULL, NULL,
+		    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
+		    ZIO_FLAG_GODFATHER);
+	}
 
 	/*
 	 * Create the root vdev.
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index e4f1271d3..844b909fb 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1474,7 +1474,7 @@ zio_nowait(zio_t *zio)
 		 */
 		spa_t *spa = zio->io_spa;
 
-		zio_add_child(spa->spa_async_zio_root, zio);
+		zio_add_child(spa->spa_async_zio_root[CPU_SEQID], zio);
 	}
 
 	__zio_execute(zio);