PING**2 On Sun, Jul 24, 2016 at 4:45 PM, Janne Blomqvist <blomqvist.ja...@gmail.com> wrote: > Hi, > > the attached patch replaces the current random_number / random_seed > implementations with an implementation that better supports threads. > It's an improved version of the RFC patch I posted earlier at > https://gcc.gnu.org/ml/gcc-patches/2015-12/msg02110.html . Please see > that earlier message for a longer-winded explanation of what's wrong > with the current implementation and how the patch addresses this. > > In short, with the patch the random number generator state is now > per-thread and stored in a per-thread (TLS) variable, enabling a > lockless fast-path. This provides up to 2 orders of magnitude better > performance on a synthetic benchmark using 4 threads, and provides a > more deterministic result as the order that threads are scheduled does > not affect the random number streams for each thread. > > Compared to the RFC patch, a number of minor and not-so-minor bugs > have been fixed, so the patch now passes the testsuite (with a few > modifications to the suite, part of the patch). Also, for REAL kinds > 4, 8, 10 the generated streams are identical (except precision, of > course) (like the current implementation), enabling precision > comparisons, as requested by Steve Kargl. However, this does not > extend to REAL(16) as that would have necessitated doubling the size > of the state, along with potential issues of slower escape from a > low-entropy state, for a feature that I believe is not used by > particularly many users in the end. So if one wants to do precision > comparisons with REAL(16) one must employ a wrapper routine. > > Regtested on x86_64-pc-linux-gnu, Ok for trunk? > > frontend ChangeLog: > > 2016-07-27 Janne Blomqvist <j...@gcc.gnu.org> > > * check.c (gfc_check_random_seed): Use new seed size in check. > * intrinsic.texi (RANDOM_NUMBER): Updated documentation. > (RANDOM_SEED): Likewise. > > > testsuite: > > 2016-07-27 Janne Blomqvist <j...@gcc.gnu.org> > > * gfortran.dg/random_7.f90: Take into account that the last seed > value is the special p value. > * gfortran.dg/random_seed_1.f90: Seed size is now constant. > > > libgfortran: > 2016-07-27 Janne Blomqvist <j...@gcc.gnu.org> > > * intrinsics/random.c: Replace KISS with xorshift1024* with > per-thread (TLS) state. > * runtime/main.c (init): Don't call random_seed_i4. > > > -- > Janne Blomqvist
-- Janne Blomqvist
