On Fri, Dec 21, 2012 at 1:25 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >> Hi, >> >> This patch adds support of atomic update of profiles counters. The goal is >> to improve >> the poor counter values for highly thread programs. >> >> The atomic update is under a new option -fprofile-gen-atomic=<N> >> N=0: default, no atomic update >> N=1: atomic update edge counters. >> N=2: atomic update some of value profile counters (currently indirect-call >> and one value profile). >> N=3: both edge counter and the above value profile counters. >> Other value: fall back to the default. >> >> This patch is a simple porting of the version in google-4_7 branch. It uses >> __atomic_fetch_add >> based on Andrew Pinski's suggestion. Note I did not apply to all the value >> profiles as >> the indirect-call profile is the most relevant one here. >> >> Test with bootstrap. >> >> Comments and suggestions are welcomed. >> >> Thanks, >> >> -Rong >> >> >> 2012-12-20 Rong Xu <x...@google.com> >> >> * libgcc/libgcov.c (__gcov_one_value_profiler_body_atomic): New >> function. Atomic update profile counters. >> (__gcov_one_value_profiler_atomic): Ditto. >> (__gcov_indirect_call_profiler_atomic): Ditto. >> * gcc/gcov-io.h: Macros for atomic update. >> * gcc/common.opt: New option. >> * gcc/tree-profile.c (gimple_init_edge_profiler): Atomic >> update profile counters. >> (gimple_gen_edge_profiler): Ditto. > > The patch looks resonable. Eventually we probably should provide rest of the > value counters > in thread safe manner. What happens on targets not having atomic operations?
>From >http://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html#_005f_005fsync-Builtins, it says: "If a particular operation cannot be implemented on the target processor, a warning is generated and a call an external function is generated. " So I think there will be a warning and eventually a link error of unsat. Thanks, -Rong > > Honza
