normal	2018-07-06 11:15:05 +0900 (Fri, 06 Jul 2018)

  New Revision: 63867

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=63867

  Log:
    thread.c (ruby_ppoll): improve timespec to msec conversion
    
    Round up non-zero <1ms timeouts to 1ms and use INT_MAX instead
    of infinite (-1) for extremely large timeouts.  All of our
    ppoll/select callers are able to handle spurious wakeups,
    anyways.
    
    This avoids excessive CPU usage and busy waits with short
    timeouts to rb_wait_for_single_fd.
    
    CPU usage with the following script is significantly reduced
    for systems with "#undef HAVE_PPOLL":
    
        require 'io/wait'
        r, w = IO.pipe
        Thread.new { loop { r.wait_readable(0.000001) } }.join(5)
        exit!(0)
    
    Low-resolution in poll(2) still sucks, though...
    
    Note: I don't see the value in making a similar change to
    time_timeval of a <1us sleep is attempted because of GVL
    release and syscall latency.

  Modified files:
    trunk/thread.c
Index: thread.c
===================================================================
--- thread.c	(revision 63866)
+++ thread.c	(revision 63867)
@@ -3971,12 +3971,13 @@ ruby_ppoll(struct pollfd *fds, nfds_t nf https://github.com/ruby/ruby/blob/trunk/thread.c#L3971
 	int tmp, tmp2;
 
 	if (ts->tv_sec > INT_MAX/1000)
-	    timeout_ms = -1;
+	    timeout_ms = INT_MAX;
 	else {
 	    tmp = (int)(ts->tv_sec * 1000);
-	    tmp2 = (int)(ts->tv_nsec / (1000 * 1000));
+	    /* round up 1ns to 1ms to avoid excessive wakeups for <1ms sleep */
+	    tmp2 = (int)((ts->tv_nsec + 999999L) / (1000L * 1000L));
 	    if (INT_MAX - tmp < tmp2)
-		timeout_ms = -1;
+		timeout_ms = INT_MAX;
 	    else
 		timeout_ms = (int)(tmp + tmp2);
 	}

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