Improve performance of zio_taskq_member

__zio_execute() calls zio_taskq_member() to determine if we are running
in a zio interrupt taskq, in which case we may need to switch to
processing this zio in a zio issue taskq.  The call to
zio_taskq_member() can become a performance bottleneck when we are
processing a high rate of zio's.

zio_taskq_member() calls taskq_member() on each of the zio interrupt
taskqs, of which there are 21.  This is slow because each call to
taskq_member() does tsd_get(taskq_tsd), which on Linux is relatively
slow.

This commit improves the performance of zio_taskq_member() by having it
cache the value of tsd_get(taskq_tsd), reducing the number of those
calls to 1/21th of the current behavior.

In a test case running `zfs send -c >/dev/null` of a filesystem with
small blocks (average 2.5KB/block), zio_taskq_member() was using 6.7% of
one CPU, and with this change it is reduced to 1.3%.  Overall time to
perform the `zfs send` reduced by 10% (~150,000 block/sec to ~165,000
blocks/sec).

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Serapheim Dimitropoulos <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Tony Nguyen <[email protected]>
Signed-off-by: Matthew Ahrens <[email protected]>
Closes #10070 

1 files changed, 3 insertions, 2 deletions

diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index cbe6fc751..bf6b5afab 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1865,14 +1865,15 @@ zio_taskq_dispatch(zio_t *zio, zio_taskq_type_t q, boolean_t cutinline)
 static boolean_t
 zio_taskq_member(zio_t *zio, zio_taskq_type_t q)
 {
-	kthread_t *executor = zio->io_executor;
 	spa_t *spa = zio->io_spa;
 
+	taskq_t *tq = taskq_of_curthread();
+
 	for (zio_type_t t = 0; t < ZIO_TYPES; t++) {
 		spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
 		uint_t i;
 		for (i = 0; i < tqs->stqs_count; i++) {
-			if (taskq_member(tqs->stqs_taskq[i], executor))
+			if (tqs->stqs_taskq[i] == tq)
 				return (B_TRUE);
 		}
 	}