From 89db85f71633e95cbaadd55b1100c01738c92557 Mon Sep 17 00:00:00 2001 From: normal Date: Thu, 13 Dec 2018 09:25:46 +0000 Subject: thread_pthread.c (native_sleep): sched_yield if GVL uncontended Uncontended GVL waitqueue could mean a single CPU setup where threads are starved and can't even insert themselves into our waitqueue. So we force other threads to run upon releasing the GVL in an uncontended state, in the hope that we can avoid entering the slow path of ppoll and similar syscalls. This should prevent test/ruby/test_thread.rb::test_signal_at_join timeout problems on our single CPU FreeBSD CI machine. [ruby-core:90417] [Bug #15398] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66381 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- thread_pthread.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) (limited to 'thread_pthread.c') diff --git a/thread_pthread.c b/thread_pthread.c index 04e938e647..f80776dbc8 100644 --- a/thread_pthread.c +++ b/thread_pthread.c @@ -2015,6 +2015,27 @@ ubf_ppoll_sleep(void *ignore) rb_thread_wakeup_timer_thread_fd(signal_self_pipe.ub_main[1]); } +/* + * Single CPU setups benefit from explicit sched_yield() before ppoll(), + * since threads may be too starved to enter the GVL waitqueue for + * us to detect contention. Instead, we want to kick other threads + * so they can run and possibly prevent us from entering slow paths + * in ppoll() or similar syscalls. + * + * Confirmed on FreeBSD 11.2 and Linux 4.19. + * [ruby-core:90417] [Bug #15398] + */ +#define GVL_UNLOCK_BEGIN_YIELD(th) do { \ + const native_thread_data_t *next; \ + rb_vm_t *vm = th->vm; \ + RB_GC_SAVE_MACHINE_CONTEXT(th); \ + rb_native_mutex_lock(&vm->gvl.lock); \ + next = gvl_release_common(vm); \ + rb_native_mutex_unlock(&vm->gvl.lock); \ + if (!next && vm_living_thread_num(vm) > 1) { \ + native_thread_yield(); \ + } + /* * This function does not exclusively acquire sigwait_fd, so it * cannot safely read from it. However, it can be woken up in @@ -2032,7 +2053,8 @@ native_ppoll_sleep(rb_thread_t *th, rb_hrtime_t *rel) th->unblock.func = ubf_ppoll_sleep; rb_native_mutex_unlock(&th->interrupt_lock); - GVL_UNLOCK_BEGIN(th); + GVL_UNLOCK_BEGIN_YIELD(th); + if (!RUBY_VM_INTERRUPTED(th->ec)) { struct pollfd pfd[2]; struct timespec ts; @@ -2066,7 +2088,7 @@ native_sleep(rb_thread_t *th, rb_hrtime_t *rel) th->unblock.func = ubf_sigwait; rb_native_mutex_unlock(&th->interrupt_lock); - GVL_UNLOCK_BEGIN(th); + GVL_UNLOCK_BEGIN_YIELD(th); if (!RUBY_VM_INTERRUPTED(th->ec)) { rb_sigwait_sleep(th, sigwait_fd, rel); -- cgit v1.2.3