Static sync thread and write issue taskq assignments

 - Given a reasonable number of syncthreads, assign each
   syncthread its own allocator.

 - Create a separate write issue taskq for a given number of
   CPUS and statically bind assign each taskq to a specified
   syncthread.

Signed-off-by: Edmund Nadolski <edmund.nadolski@ixsystems.com>

include/sys/spa.h

@@ -825,6 +825,11 @@ extern void spa_sync_allpools(void);
 
 extern uint_t zfs_sync_pass_deferred_free;
 
+/* spa sync taskqueues */
+taskq_t *spa_sync_tq_create(spa_t *spa, const char *name);
+void spa_sync_tq_destroy(spa_t *spa);
+void spa_select_allocator(zio_t *zio);
+
 /* spa namespace global mutex */
 extern kmutex_t spa_namespace_lock;
 

include/sys/spa_impl.h

@@ -188,6 +188,12 @@ typedef struct spa_taskqs {
 	taskq_t **stqs_taskq;
 } spa_taskqs_t;
 
+/* one for each thread in the spa sync taskq */
+typedef struct spa_syncthread_info {
+	kthread_t	*sti_thread;
+	taskq_t		*sti_wr_iss_tq;		/* assigned wr_iss taskq */
+} spa_syncthread_info_t;
+
 typedef enum spa_all_vdev_zap_action {
 	AVZ_ACTION_NONE = 0,
 	AVZ_ACTION_DESTROY,	/* Destroy all per-vdev ZAPs and the AVZ. */
@@ -264,6 +270,10 @@ struct spa {
 	spa_alloc_t	*spa_allocs;
 	int		spa_alloc_count;
 
+	/* per-allocator sync thread taskqs */
+	taskq_t		*spa_sync_tq;
+	spa_syncthread_info_t *spa_syncthreads;
+
 	spa_aux_vdev_t	spa_spares;		/* hot spares */
 	spa_aux_vdev_t	spa_l2cache;		/* L2ARC cache devices */
 	nvlist_t	*spa_label_features;	/* Features for reading MOS */
@@ -455,7 +465,7 @@ extern char *spa_config_path;
 extern const char *zfs_deadman_failmode;
 extern uint_t spa_slop_shift;
 extern void spa_taskq_dispatch_ent(spa_t *spa, zio_type_t t, zio_taskq_type_t q,
-    task_func_t *func, void *arg, uint_t flags, taskq_ent_t *ent);
+    task_func_t *func, void *arg, uint_t flags, taskq_ent_t *ent, zio_t *zio);
 extern void spa_taskq_dispatch_sync(spa_t *, zio_type_t t, zio_taskq_type_t q,
     task_func_t *func, void *arg, uint_t flags);
 extern void spa_load_spares(spa_t *spa);

include/sys/zio.h

@@ -223,6 +223,9 @@ typedef uint64_t zio_flag_t;
 #define	ZIO_FLAG_REEXECUTED	(1ULL << 29)
 #define	ZIO_FLAG_DELEGATED	(1ULL << 30)
 
+#define	ZIO_ALLOCATOR_NONE	(-1)
+#define	ZIO_HAS_ALLOCATOR(zio)	((zio)->io_allocator != ZIO_ALLOCATOR_NONE)
+
 #define	ZIO_FLAG_MUSTSUCCEED		0
 #define	ZIO_FLAG_RAW	(ZIO_FLAG_RAW_COMPRESS | ZIO_FLAG_RAW_ENCRYPT)
 
@@ -526,6 +529,9 @@ struct zio {
 
 	/* Taskq dispatching state */
 	taskq_ent_t	io_tqent;
+
+	/* write issue taskq selection, based upon sync thread */
+	taskq_t		*io_wr_iss_tq;
 };
 
 enum blk_verify_flag {

man/man4/zfs.4

@@ -1971,13 +1971,6 @@ and may need to load new metaslabs to satisfy these allocations.
 .It Sy zfs_sync_pass_rewrite Ns = Ns Sy 2 Pq uint
 Rewrite new block pointers starting in this pass.
 .
-.It Sy zfs_sync_taskq_batch_pct Ns = Ns Sy 75 Ns % Pq int
-This controls the number of threads used by
-.Sy dp_sync_taskq .
-The default value of
-.Sy 75%
-will create a maximum of one thread per CPU.
-.
 .It Sy zfs_trim_extent_bytes_max Ns = Ns Sy 134217728 Ns B Po 128 MiB Pc Pq uint
 Maximum size of TRIM command.
 Larger ranges will be split into chunks no larger than this value before

module/zfs/dbuf.c

@@ -4587,7 +4587,10 @@ dbuf_sync_leaf(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
 	}
 }
 
-/* May be called recursively from dbuf_sync_indirect(). */
+/*
+ * Syncs out a range of dirty records for indirect or leaf dbufs.  May be
+ * called recursively from dbuf_sync_indirect().
+ */
 void
 dbuf_sync_list(list_t *list, int level, dmu_tx_t *tx)
 {

module/zfs/dsl_pool.c

@@ -209,8 +209,7 @@ dsl_pool_open_impl(spa_t *spa, uint64_t txg)
 	txg_list_create(&dp->dp_early_sync_tasks, spa,
 	    offsetof(dsl_sync_task_t, dst_node));
 
-	dp->dp_sync_taskq = taskq_create("dp_sync_taskq",
-	    MIN(spa->spa_alloc_count, boot_ncpus), minclsyspri, 1, INT_MAX, 0);
+	dp->dp_sync_taskq = spa_sync_tq_create(spa, "dp_sync_taskq");
 
 	dp->dp_zil_clean_taskq = taskq_create("dp_zil_clean_taskq",
 	    zfs_zil_clean_taskq_nthr_pct, minclsyspri,
@@ -403,7 +402,7 @@ dsl_pool_close(dsl_pool_t *dp)
 	txg_list_destroy(&dp->dp_dirty_dirs);
 
 	taskq_destroy(dp->dp_zil_clean_taskq);
-	taskq_destroy(dp->dp_sync_taskq);
+	spa_sync_tq_destroy(dp->dp_spa);
 
 	/*
 	 * We can't set retry to TRUE since we're explicitly specifying