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| author | René Scharfe <l.s.r@web.de> | 2020-06-24 15:05:38 +0200 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2020-06-24 09:09:44 -0700 |
| commit | 23c4319f0d1bd68a15368e97a4612768333ff486 (patch) | |
| tree | 27964280b803234451472ad993626487f88dbe72 /revision.h | |
| parent | c9c318d6bf26bcecdca5b6f31683b9d5887a83ee (diff) | |
| download | git-23c4319f0d1bd68a15368e97a4612768333ff486.tar.gz | |
revision: reallocate TOPO_WALK object flags
The bit fields in struct object have an unfortunate layout. Here's what
pahole reports on x86_64 GNU/Linux:
struct object {
unsigned int parsed:1; /* 0: 0 4 */
unsigned int type:3; /* 0: 1 4 */
/* XXX 28 bits hole, try to pack */
/* Force alignment to the next boundary: */
unsigned int :0;
unsigned int flags:29; /* 4: 0 4 */
/* XXX 3 bits hole, try to pack */
struct object_id oid; /* 8 32 */
/* size: 40, cachelines: 1, members: 4 */
/* sum members: 32 */
/* sum bitfield members: 33 bits, bit holes: 2, sum bit holes: 31 bits */
/* last cacheline: 40 bytes */
};
Notice the 1+3+29=33 bits in bit fields and 28+3=31 bits in holes.
There are holes inside the flags bit field as well -- while some object
flags are used for more than one purpose, 22, 23 and 24 are still free.
Use 23 and 24 instead of 27 and 28 for TOPO_WALK_EXPLORED and
TOPO_WALK_INDEGREE. This allows us to reduce FLAG_BITS by one so that
all bitfields combined fit into a single 32-bit slot:
struct object {
unsigned int parsed:1; /* 0: 0 4 */
unsigned int type:3; /* 0: 1 4 */
unsigned int flags:28; /* 0: 4 4 */
struct object_id oid; /* 4 32 */
/* size: 36, cachelines: 1, members: 4 */
/* last cacheline: 36 bytes */
};
With this tight packing the size of struct object is reduced by 10%.
Other architectures probably benefit as well.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'revision.h')
| -rw-r--r-- | revision.h | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/revision.h b/revision.h index 93491b79d4..f412ae85eb 100644 --- a/revision.h +++ b/revision.h @@ -37,6 +37,10 @@ /* WARNING: This is also used as REACHABLE in commit-graph.c. */ #define PULL_MERGE (1u<<15) + +#define TOPO_WALK_EXPLORED (1u<<23) +#define TOPO_WALK_INDEGREE (1u<<24) + /* * Indicates object was reached by traversal. i.e. not given by user on * command-line or stdin. @@ -48,9 +52,6 @@ #define TRACK_LINEAR (1u<<26) #define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | PULL_MERGE) -#define TOPO_WALK_EXPLORED (1u<<27) -#define TOPO_WALK_INDEGREE (1u<<28) - #define DECORATE_SHORT_REFS 1 #define DECORATE_FULL_REFS 2 |