BRT: Skip getting length in brt_entry_lookup()

Unlike DDT, where ZAP values may have different lengths due to
compression, all BRT entries are identical 8-byte counters.  It
does not make sense to first fetch the length only to assert it.
zap_lookup_uint64() is specifically designed to work with counters
of different size and should return error if something odd found.
Calling it straight allows to save some measurable CPU time.

Reviewed-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #15950

diff --git a/module/zfs/brt.c b/module/zfs/brt.c
index 5d1f4728b6453ab452893e47273eff52470c59ba..ea8c0735c4b7645b8b12dc24f2f08b35791f4ac1 100644 (file)
--- a/module/zfs/brt.c
+++ b/module/zfs/brt.c
@@ -900,7 +900,6 @@ static int
 brt_entry_lookup(brt_t *brt, brt_vdev_t *brtvd, brt_entry_t *bre)
 {
        uint64_t mos_entries;
-       uint64_t one, physsize;
        int error;
 
        ASSERT(RW_LOCK_HELD(&brt->brt_lock));
@@ -918,21 +917,8 @@ brt_entry_lookup(brt_t *brt, brt_vdev_t *brtvd, brt_entry_t *bre)
 
        brt_unlock(brt);
 
-       error = zap_length_uint64(brt->brt_mos, mos_entries, &bre->bre_offset,
-           BRT_KEY_WORDS, &one, &physsize);
-       if (error == 0) {
-               ASSERT3U(one, ==, 1);
-               ASSERT3U(physsize, ==, sizeof (bre->bre_refcount));
-
-               error = zap_lookup_uint64(brt->brt_mos, mos_entries,
-                   &bre->bre_offset, BRT_KEY_WORDS, 1,
-                   sizeof (bre->bre_refcount), &bre->bre_refcount);
-               BRT_DEBUG("ZAP lookup: object=%llu vdev=%llu offset=%llu "
-                   "count=%llu error=%d", (u_longlong_t)mos_entries,
-                   (u_longlong_t)brtvd->bv_vdevid,
-                   (u_longlong_t)bre->bre_offset,
-                   error == 0 ? (u_longlong_t)bre->bre_refcount : 0, error);
-       }
+       error = zap_lookup_uint64(brt->brt_mos, mos_entries, &bre->bre_offset,
+           BRT_KEY_WORDS, 1, sizeof (bre->bre_refcount), &bre->bre_refcount);
 
        brt_wlock(brt);