svn commit: r349822 - stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs
Alexander Motin
mav at FreeBSD.org
Sun Jul 7 18:42:27 UTC 2019
Author: mav
Date: Sun Jul 7 18:42:25 2019
New Revision: 349822
URL: https://svnweb.freebsd.org/changeset/base/349822
Log:
MFC r349040: Minimize aggsum_compare(&arc_size, arc_c) calls.
For busy ARC situation when arc_size close to arc_c is desired. But
then it is quite likely that aggsum_compare(&arc_size, arc_c) will need
to flush per-CPU buckets to find exact comparison result. Doing that
often in a hot path penalizes whole idea of aggsum usage there, since it
replaces few simple atomic additions with dozens of lock acquisitions.
Replacing aggsum_compare() with aggsum_upper_bound() in code increasing
arc_p when ARC is growing (arc_size < arc_c) according to PMC profiles
allows to save ~5% of CPU time in aggsum code during sequential write
to 12 ZVOLs with 16KB block size on large dual-socket system.
I suppose there some minor arc_p behavior change due to lower precision
of the new code, but I don't think it is a big deal, since it should
affect only very small window in time (aggsum buckets are flushed every
second) and in ARC size (buckets are limited to 10 average ARC blocks
per CPU).
Modified:
stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
Directory Properties:
stable/12/ (props changed)
Modified: stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
==============================================================================
--- stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c Sun Jul 7 18:40:35 2019 (r349821)
+++ stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c Sun Jul 7 18:42:25 2019 (r349822)
@@ -5269,7 +5269,7 @@ arc_get_data_impl(arc_buf_hdr_t *hdr, uint64_t size, v
* If we are growing the cache, and we are adding anonymous
* data, and we have outgrown arc_p, update arc_p
*/
- if (aggsum_compare(&arc_size, arc_c) < 0 &&
+ if (aggsum_upper_bound(&arc_size) < arc_c &&
hdr->b_l1hdr.b_state == arc_anon &&
(refcount_count(&arc_anon->arcs_size) +
refcount_count(&arc_mru->arcs_size) > arc_p))
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