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authorLibravatar René Scharfe <l.s.r@web.de>2020-06-24 15:05:38 +0200
committerLibravatar Junio C Hamano <gitster@pobox.com>2020-06-24 09:09:44 -0700
commit23c4319f0d1bd68a15368e97a4612768333ff486 (patch)
tree27964280b803234451472ad993626487f88dbe72 /po
parentThe fourth batch (diff)
downloadtgif-23c4319f0d1bd68a15368e97a4612768333ff486.tar.xz
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 'po')
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