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thread.c (ruby_ppoll): improve timespec to msec conversion

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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.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63867 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
normal 2018-07-06 02:15:05 +00:00
parent 24aa7a13ca
commit fcf8c622fd
1 changed files with 4 additions and 3 deletions
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7
thread.c
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@ -3971,12 +3971,13 @@ ruby_ppoll(struct pollfd *fds, nfds_t nfds,
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);
}