Junio C Hamano wrote:
> 4-way cuckoo
Cool stuff!
While looking at the performance of it, I noticed something odd about
packing: stracing the command you gave for your timings
strace -o pack.trace \
./git-pack-objects --count-only --keep-true-parents --honor-pack-keep \
--non-empty --all --reflog --no-reuse-delta --delta-base-offset \
--stdout </dev/null >/dev/null
yields the fairly crazy
$ grep -c 'open.*attrib' pack.trace
4398
including runs such as (with a line of context for clarity)
munmap(0x7f9cd39f7000, 4096) = 0
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("compat/.gitattributes", O_RDONLY) = -1 ENOENT (No such file or directory)
open("t/.gitattributes", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=36, ...}) = 0
So calling git_checkattr in a loop is quite inefficient. Indeed
there's a good optimization opportunity: compiled for 4-way hashing I
have (best of 3)
6.76user 0.23system 0:07.02elapsed 99%CPU (0avgtext+0avgdata 479792maxresident)
but making no_try_delta() in pack-objects.c a dummy 'return 0' gives
6.45user 0.13system 0:06.61elapsed 99%CPU (0avgtext+0avgdata 478256maxresident)
Which would be a 4.5% speedup. Obviously that won't quite be
attainable since we want the attributes mechanism to work, but we
still shouldn't have to open 4398 .gitattributes files when there are
only 8 .gitattributes plus one .git/info/attributes.
--
Thomas Rast
trast@{inf,student}.ethz.ch
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