MINOR: poller: update_fd_polling: wake a random other thread
When enabling an FD that's only bound to another thread, instead of
always picking the first one, let's pick a random one. This is rarely
used (enabling a frontend, or session rate-limiting period ending),
and has greater chances of avoiding that some obscure corner cases
could degenerate into a poorly distributed load.
diff --git a/src/fd.c b/src/fd.c
index 426afb5..56fa292 100644
--- a/src/fd.c
+++ b/src/fd.c
@@ -449,9 +449,11 @@
fd_add_to_fd_list(&update_list, fd, offsetof(struct fdtab, update));
if (fd_active(fd) && !(fdtab[fd].thread_mask & tid_bit)) {
- /* we need to wake up one thread to handle it immediately */
- int thr = my_ffsl(fdtab[fd].thread_mask & ~tid_bit & all_threads_mask) - 1;
-
+ /* we need to wake up another thread to handle it immediately, any will fit,
+ * so let's pick a random one so that it doesn't always end up on the same.
+ */
+ int thr = one_among_mask(fdtab[fd].thread_mask & all_threads_mask,
+ statistical_prng_range(MAX_THREADS));
wake_thread(thr);
}
}