On Feb 23 16:05, Ken Brown wrote: > On 2/21/2019 6:52 PM, Ken Brown wrote: > > When emacs is built, it detects the timerfd functions and uses them if > > they're > > found. Now that Cygwin has these functions, the resulting build of emacs is > > very slow to respond to user input. If I press a key, there is a 1-2 second > > delay before emacs responds. > > > > I can work around this by configuring emacs with emacs_cv_have_timerfd=no, > > but > > it would be nice to find the cause. I'll try to make an STC, but I thought > > I'd > > report it here in the meantime, in case anyone has ideas or debugging > > suggestions. > > I don't have an STC yet, but if I start emacs and then attach gdb to it at > random times, the backtrace always look like this: > > #0 0x00007ffbb192b4f4 in ntdll!ZwWaitForMultipleObjects () > from /c/WINDOWS/SYSTEM32/ntdll.dll > #1 0x00007ffbadf56099 in WaitForMultipleObjectsEx () > from /c/WINDOWS/System32/KERNELBASE.dll'' > #2 0x00007ffbadf55f8e in WaitForMultipleObjects () > from /c/WINDOWS/System32/KERNELBASE.dll > #3 0x0000000180159f9d in timerfd_tracker::wait (this=this@entry=0x1803a22c0, > nonblocking=false) > at /usr/src/debug/cygwin-3.0.1-1/winsup/cygwin/timerfd.cc:448 > #4 0x00000001800a7b0e in fhandler_timerfd::read (this=<optimized out>, > ptr=0xffffba30, len=@0xffffb9b0: 8) > at /usr/src/debug/cygwin-3.0.1-1/winsup/cygwin/fhandler_timerfd.cc:134 > [...] > > This suggests to me that the slowdown comes from timerfd_tracker::wait. > > The context is that emacs creates a timerfd timer that expires every 2 > seconds, > 'select' waits for the timer's file descriptor to be ready for reading, and > then > emacs calls 'read'.
Below's the NSSTC I used to test my timerfd implementation (based on
another STC to show a problem in POSIX timers). From what I can tell it
works as desired. If you find a problem, please point it out or send a
patch.
Thanks,
Corinna
#define _GNU_SOURCE 1
#include <sys/timerfd.h>
#include <sys/select.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h> /* Definition of uint64_t */
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
static void
print_elapsed_time (void)
{
static struct timespec start;
struct timespec curr;
static int first_call = 1;
int secs, nsecs;
if (first_call)
{
first_call = 0;
if (clock_gettime (CLOCK_REALTIME, &start) == -1)
handle_error ("clock_gettime");
}
if (clock_gettime (CLOCK_REALTIME, &curr) == -1)
handle_error ("clock_gettime");
secs = curr.tv_sec - start.tv_sec;
nsecs = curr.tv_nsec - start.tv_nsec;
if (nsecs < 0)
{
secs--;
nsecs += 1000000000;
}
printf ("%d.%03d: ", secs, (nsecs + 500000) / 1000000);
}
int
main (int argc, char *argv[])
{
struct itimerspec new_value;
int max_exp, fd;
struct timespec now;
uint64_t exp, tot_exp;
ssize_t s;
fd_set fds;
int status;
int i;
if ((argc != 2) && (argc != 4) && argc != 5)
{
fprintf (stderr, "%s init-secs [interval-secs max-exp]\n", argv[0]);
exit (EXIT_FAILURE);
}
if (clock_gettime (CLOCK_MONOTONIC, &now) == -1)
handle_error ("clock_gettime");
/* Create a CLOCK_MONOTONIC absolute timer with initial
expiration and interval as specified in command line */
new_value.it_value.tv_sec = atoi (argv[1]) + now.tv_sec;
new_value.it_value.tv_nsec = now.tv_nsec;
if (argc == 2)
{
new_value.it_interval.tv_sec = 0;
max_exp = 1;
}
else
{
new_value.it_interval.tv_sec = atoi (argv[2]);
max_exp = atoi (argv[3]);
}
new_value.it_interval.tv_nsec = 0;
if (argc == 5)
{
#if 1
char buf[128];
sprintf (buf, "ls -l /proc/%d/fd", getpid ());
system (buf);
#endif
fd = atoi (argv[4]);
goto machhinne;
}
fd = timerfd_create (CLOCK_MONOTONIC, 0);
if (fd == -1)
handle_error ("timerfd_create");
if (timerfd_settime (fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1)
handle_error ("timerfd_settime");
#if 0
switch (fork ())
{
case -1:
perror ("fork");
break;
case 0:
{
char buf[128];
sprintf (buf, "ls -l /proc/%d/fd", getpid ());
system (buf);
}
break;
default:
break;
}
#elif 0
switch (fork ())
{
case 0:
{
char buf[16];
printf ("child %d\n", getpid ());
snprintf (buf, sizeof buf, "%d", fd);
execl ("./timerfd", argv[0], argv[1], argv[2], argv[3], buf, NULL);
perror ("execl");
}
break;
case -1:
perror ("fork");
return 0;
default:
printf ("parent %d\n", getpid ());
break;
}
#endif
machhinne:
print_elapsed_time ();
printf ("timer started %d\n", getpid ());
for (i = 0, tot_exp = 0; tot_exp < max_exp; ++i)
{
#if 1
int ret;
FD_ZERO (&fds);
FD_SET (fd, &fds);
ret = select (fd + 1, &fds, NULL, NULL, NULL);
if (ret < 0)
perror ("select");
if (!FD_ISSET (fd, &fds))
continue;
#endif
s = read (fd, &exp, sizeof (uint64_t));
if (s != sizeof (uint64_t))
handle_error ("read");
tot_exp += exp;
print_elapsed_time ();
printf ("%d read: %llu; total=%llu\n",
getpid (),
(unsigned long long) exp, (unsigned long long) tot_exp);
}
wait (&status);
exit (EXIT_SUCCESS);
}
--
Corinna Vinschen
Cygwin Maintainer
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