sorry for duplicate, webmail fail. On Wed, Feb 12, 2014 at 5:41 PM, Sébastien Villemot <sebast...@debian.org>wrote:
> Le mardi 04 février 2014 à 23:17 +0100, Julian Taylor a écrit : > > There are well known issues with the gnu openmp variant of openblas in > > respect to forks of applications. > > Please find attached an example of such a breakage, using > parallelisation in R. The example is run simply with: > > R --vanilla < foo.R > > On sid, with openblas 0.2.8-3 (OpenMP), the program runs and reports 8 > condition numbers. > > On sid but with openblas 0.2.8-2 (pthreads), the program hangs. > > thanks, it hangs because R forks: strace -e clone ... > mclapply(z, f, mc.cores = num.cores) clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f6df0cd9a50) = 28886 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f6df0cd9a50) = 28887 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f6df0cd9a50) = 28888 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f6df0cd9a50) = 28889 this is the same issue that plagues python and that can be fixed with pthreads but not gnu openmp. As I'm not familiar with R, can you construct a testcase where openblas is used in both the parent and the child of the fork? It should also hang with openmp.
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