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authorMatthew Ahrens <[email protected]>2017-04-13 14:35:00 -0700
committerBrian Behlendorf <[email protected]>2017-04-24 10:44:19 -0700
commita00433837236507e6ce90c22bf09e6699deef991 (patch)
tree828b79a98f4b1963cd96dfad0cf91ccac43b490d /module/zfs
parent321204bec61042d7785e1aa3c3362529e8e8373b (diff)
OpenZFS 8025 - dbuf_read() creates unnecessary zio_root() for bonus buf
Authored by: Matthew Ahrens <[email protected]> Reviewed by: Dan Kimmel <[email protected]> Reviewed by: Pavel Zakharov <[email protected]> Reviewed by: Prashanth Sreenivasa <[email protected]> Approved by: Robert Mustacchi <[email protected]> Ported-by: Brian Behlendorf <[email protected]> dbuf_read() creates a zio_root() to track and wait for all the zio's that may happen as part of this call. However, if the blkptr_t for this buffer is NULL or a hole, we will not create any more zio's, so this zio_root() is unnecessary. This is always the case when calling dbuf_read() on a bonus buffer, because it has no blkptr (it's part of the containing dnode). For workloads that read a lot of bonus buffers (e.g. file creation and removal), creating and destroying these unnecessary zio's can decrease performance by around 3%. The fix is to only create/destroy the zio_root() in dbuf_read() if the blkptr is not NULL and not a hole. Porting Notes: - The error handling for when dbuf_read_impl() fails which was originally added in commit 5f6d0b6f5 has been preserved. OpenZFS-issue: https://www.illumos.org/issues/8025 OpenZFS-commit: https://github.com/openzfs/openzfs/commit/8ec5c7c Closes #6048
Diffstat (limited to 'module/zfs')
-rw-r--r--module/zfs/dbuf.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index 096d18358..b0b1bffab 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -1170,7 +1170,6 @@ int
dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
{
int err = 0;
- boolean_t havepzio = (zio != NULL);
boolean_t prefetch;
dnode_t *dn;
@@ -1214,11 +1213,13 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
DB_DNODE_EXIT(db);
} else if (db->db_state == DB_UNCACHED) {
spa_t *spa = dn->dn_objset->os_spa;
+ boolean_t need_wait = B_FALSE;
if (zio == NULL &&
- db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr))
+ db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr)) {
zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
-
+ need_wait = B_TRUE;
+ }
err = dbuf_read_impl(db, zio, flags);
/* dbuf_read_impl has dropped db_mtx for us */
@@ -1230,7 +1231,7 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
rw_exit(&dn->dn_struct_rwlock);
DB_DNODE_EXIT(db);
- if (!err && !havepzio && zio != NULL)
+ if (!err && need_wait)
err = zio_wait(zio);
} else {
/*
@@ -1265,7 +1266,6 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
mutex_exit(&db->db_mtx);
}
- ASSERT(err || havepzio || db->db_state == DB_CACHED);
return (err);
}