Avoid extra work updating ARC kstats and tunables

After e357046 it should not be necessary to periodically update ARC
kstats and tunables.  Tunable updates are applied when modified, and
kstats are updated on demand.

Update kstats in `arc_evict_cb_check()` for `ZFS_DEBUG` builds only.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ryan Moeller <[email protected]>
Closes #11237 

1 files changed, 9 insertions, 16 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 8519eda30..e05b11d51 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -4882,14 +4882,7 @@ arc_kmem_reap_soon(void)
 static boolean_t
 arc_evict_cb_check(void *arg, zthr_t *zthr)
 {
-	/*
-	 * This is necessary so that any changes which may have been made to
-	 * many of the zfs_arc_* module parameters will be propagated to
-	 * their actual internal variable counterparts. Without this,
-	 * changing those module params at runtime would have no effect.
-	 */
-	arc_tuning_update(B_FALSE);
-
+#ifdef ZFS_DEBUG
 	/*
 	 * This is necessary in order to keep the kstat information
 	 * up to date for tools that display kstat data such as the
@@ -4897,15 +4890,15 @@ arc_evict_cb_check(void *arg, zthr_t *zthr)
 	 * typically do not call kstat's update function, but simply
 	 * dump out stats from the most recent update.  Without
 	 * this call, these commands may show stale stats for the
-	 * anon, mru, mru_ghost, mfu, and mfu_ghost lists. Even
-	 * with this change, the data might be up to 1 second
-	 * out of date(the arc_evict_zthr has a maximum sleep
-	 * time of 1 second); but that should suffice.  The
-	 * arc_state_t structures can be queried directly if more
-	 * accurate information is needed.
+	 * anon, mru, mru_ghost, mfu, and mfu_ghost lists.  Even
+	 * with this call, the data might be out of date if the
+	 * evict thread hasn't been woken recently; but that should
+	 * suffice.  The arc_state_t structures can be queried
+	 * directly if more accurate information is needed.
 	 */
 	if (arc_ksp != NULL)
 		arc_ksp->ks_update(arc_ksp, KSTAT_READ);
+#endif
 
 	/*
 	 * We have to rely on arc_wait_for_eviction() to tell us when to
@@ -7675,8 +7668,8 @@ arc_init(void)
 		kstat_install(arc_ksp);
 	}
 
-	arc_evict_zthr = zthr_create_timer("arc_evict",
-	    arc_evict_cb_check, arc_evict_cb, NULL, SEC2NSEC(1));
+	arc_evict_zthr = zthr_create("arc_evict",
+	    arc_evict_cb_check, arc_evict_cb, NULL);
 	arc_reap_zthr = zthr_create_timer("arc_reap",
 	    arc_reap_cb_check, arc_reap_cb, NULL, SEC2NSEC(1));