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| author | Theodore Ts'o <tytso@mit.edu> | 2012-02-06 10:00:17 +0400 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2012-02-06 12:15:12 +0400 |
| commit | f2d713fc3e8e0b7be89584f04b421808aa99c403 (patch) | |
| tree | f648f664829a3cb9351a14798227907a9b83e6c8 /INSTALL | |
| parent | 828ea97de486c1693d6e4f2c7347acb50235a85d (diff) | |
Fix build problems related to profile-directed optimization
There was a number of problems I ran into when trying the
profile-directed optimizations added by Andi Kleen in git commit
7ddc2710b9. (This was using gcc 4.4 found on many enterprise
distros.)
1) The -fprofile-generate and -fprofile-use commands are incompatible
with ccache; the code ends up looking in the wrong place for the gcda
files based on the ccache object names.
2) If the makefile notices that CFLAGS are different, it will rebuild
all of the binaries. Hence the recipe originally specified by the
INSTALL file ("make profile-all" followed by "make install") doesn't
work. It will appear to work, but the binaries will end up getting
built with no optimization.
This patch fixes this by using an explicit set of options passed via
the PROFILE variable then using this to directly manipulate CFLAGS and
EXTLIBS.
The developer can run "make PROFILE=BUILD all ; sudo make
PROFILE=BUILD install" automatically run a two-pass build with the
test suite run in between as the sample workload for the purpose of
recording profiling information to do the profile-directed
optimization.
Alternatively, the profiling version of binaries can be built using:
make PROFILE=GEN PROFILE_DIR=/var/cache/profile all
make PROFILE=GEN install
and then after git has been used for a while, the optimized version of
the binary can be built as follows:
make PROFILE=USE PROFILE_DIR=/var/cache/profile all
make PROFILE=USE install
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'INSTALL')
| -rw-r--r-- | INSTALL | 17 |
1 files changed, 13 insertions, 4 deletions
@@ -28,16 +28,25 @@ set up install paths (via config.mak.autogen), so you can write instead If you're willing to trade off (much) longer build time for a later faster git you can also do a profile feedback build with - $ make profile-all - # make prefix=... install + $ make prefix=/usr PROFILE=BUILD all + # make prefix=/usr PROFILE=BUILD install This will run the complete test suite as training workload and then rebuild git with the generated profile feedback. This results in a git which is a few percent faster on CPU intensive workloads. This may be a good tradeoff for distribution packagers. -Note that the profile feedback build stage currently generates -a lot of additional compiler warnings. +Or if you just want to install a profile-optimized version of git into +your home directory, you could run: + + $ make PROFILE=BUILD install + +As a caveat: a profile-optimized build takes a *lot* longer since the +git tree must be built twice, and in order for the profiling +measurements to work properly, ccache must be disabled and the test +suite has to be run using only a single CPU. In addition, the profile +feedback build stage currently generates a lot of additional compiler +warnings. Issues of note: |