Date: Tue, 29 Dec 1998 10:22:42 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender: eliz AT is
To: Robert Hoehne <robert DOT hoehne AT gmx DOT net>
cc: Peter Palotas <blizzar AT hem1 DOT passagen DOT se>, djgpp-workers AT delorie DOT com
Subject: Re: Profiling Problems.
In-Reply-To: <368807D0.A8B5E4F2@gmx.net>
Message-ID: <Pine.SUN.3.91.981229102214.15836O-100000@is>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Reply-To: djgpp-workers AT delorie DOT com


On Mon, 28 Dec 1998, Robert Hoehne wrote:

> Eli Zaretskii wrote :
> > 
> > Please try the version of itimer.c attached below.  It is NOT TESTED (I
> 
> This version of itimer.c seems to fix the bug. It works on both, W95
> and raw DOS.

Here's the final version of itimer.c that I suggest (DJ, I'm sending
the diffs against the last v2.02 upload in a separate message).

This version is tested on DOS 5.0 and on Windows 95, both by profiling
a (quite trivial) program and with a modified test program from
djtst202 which sets up two timers at once.  See my other mail for the
source of the test program I used.

I found quite a lot of things I couldn't explain/understand/justify in
the original source, and since I don't know Tom Demmer's new email
address, I cannot ask him to comment.  So please read this version
carefully, compare it to the previous version, and try to find any
bugs in what I changed or what I left unchanged.  I added extensive
commentary in a few subtle places, to make them less obscure and
easier to understand.

I'm in particular curious why did Tom require the current `uclock'
value to be 65536L *after* the actual expiration time, before raising
the appropriate signal.  Tom clearly did that on purpose, but the
effect seems to be negative in all the cases I tested, and I couldn't
find any case where Tom's version preformed better.  So I removed the
addition of 65536L; but if anybody can explain it, I'd love to hear.

> BTW: The itimer.c from DJGPP 2.01 worked also on both. At least under
> W95 it produced some realistic profiling information but I have not
> checked if it works correct.

The reason for the changes in itimer was that the version in v2.01
didn't support two timers at the same time.  So, e.g., if your program
used SIGALRM, you couldn't profile it.  Tom's implementation adds a
scheduler which arbitrates between the two timers and raises an
appropriate signal as needed.

----------------------------------------------------------------
/* Copyright (C) 1995 Charles Sandmann (sandmann AT clio DOT rice DOT edu)
   setitimer implmentation - used for profiling and alarm
   BUGS: ONLY ONE AT A TIME, first pass code
   This software may be freely distributed, no warranty.

   Changed to work with SIGALRM & SIGPROF by Tom Demmer.
   Gotchas:
     - It relies on uclock(), which does not work under Windows 95.
     - It screws up debuggers for reasons I cannot figure out.
     - Both is true for the old version, too.
*/

#include <libc/stubs.h>
#include <sys/time.h>
#include <errno.h>
#include <dpmi.h>
#include <signal.h>
#include <go32.h>

static uclock_t r_exp, r_rel,  /* When REAL expires & reload value */
                p_exp, p_rel;  /* When PROF expires & reload value */

static uclock_t u_now;

int
getitimer(int which, struct itimerval *value)
{
  uclock_t expire, reload;

  u_now = uclock();
  if (which == ITIMER_REAL)
  {
    if (r_exp)
    {
      expire = r_exp - u_now;
      reload = r_rel;
    }
    else
      expire = reload = 0;
  }
  else if (which == ITIMER_PROF)
  {
    if (p_exp)
    {
      expire = p_exp - u_now;
      reload = p_rel;
    }
    else
      expire = reload = 0;
  }
  else
  {
    errno = EINVAL;
    return -1;
  }
  value->it_value.tv_sec    = expire / UCLOCKS_PER_SEC;
  value->it_value.tv_usec   = (expire % UCLOCKS_PER_SEC)*3433/4096;
  value->it_interval.tv_sec = reload / UCLOCKS_PER_SEC;
  value->it_interval.tv_usec= (reload % UCLOCKS_PER_SEC)*3433/4096;
  return 0;
}

extern unsigned __djgpp_timer_countdown;
extern __dpmi_paddr __djgpp_old_timer;
extern int __djgpp_timer_hdlr;
static char timer_on = 0;

/* Set back IRQ2 handler to default values and disable own signal
   handler */
static void
stop_timer(void)
{
  if(!timer_on)
    return;
  __djgpp_timer_countdown = -1;
  __dpmi_set_protected_mode_interrupt_vector(8, &__djgpp_old_timer);
  timer_on = 0;
  signal(SIGTIMR, SIG_DFL);
}

/* Returns the time to the next event in UCLOCK_PER_SEC u_now must be
   set by calling routine.  Return 0 if no event pending. */

static inline uclock_t
GetNextEvent(void)
{
  if (r_exp && p_exp)
     return (r_exp < p_exp ? r_exp - u_now : p_exp - u_now );
  else if (r_exp)
     return  r_exp - u_now;
  else if (p_exp)
     return p_exp - u_now;
  else
     return 0;
}

/* Handler for SIGTIMR */
static void
timer_action(int signum)
{
  int do_tmr=0,do_prof=0;
  uclock_t next;

  u_now = uclock();

  /* Check the real timer */
  if (r_exp && (r_exp <= u_now) )
  {
    do_tmr = 1;
    if (r_rel)
      r_exp += r_rel;
    else
      r_exp = 0;
  }

  /* Check profile timer */
  if (p_exp && (p_exp <= u_now))
  {
    do_prof = 1;
    if (p_rel)
      p_exp += p_rel;
    else
      p_exp = 0;
  }

  /* Now we have to schedule the next interrupt, if any pending */
  if (do_tmr || do_prof)
  {
    if ((next = GetNextEvent()) != 0)
    {
      next /= 65536L;
      /* Why do I subtract 1 from NEXT below?  Because the timer
	 interrupt handler (see exceptn.S) checks whether the
	 countdown variable is zero *before* it decrements it.  So
	 setting it to zero means the timer will expire on the next
	 tick, which is exactly what we want.

	 Note also that NEXT might be negative if the timer just
	 fired, and if the reload value is smaller than u_now - X_exp.
	 We treat that as if NEXT were zero, meaning that the timer
	 will expire on the next tick.  */
      __djgpp_timer_countdown = next > 0 ? next - 1 : 0 ;
    }
    else
      stop_timer();

    if (do_tmr)
      raise(SIGALRM);
    if (do_prof)
      raise(SIGPROF);
  }
}

static void
start_timer(void)
{
  uclock_t next;
  __dpmi_paddr int8;

  next = GetNextEvent();
  next /= 65536L;
  /* See the commentary above about subtracting 1 from NEXT, and about
     negative values being returned by GetNextEvent.  */
  __djgpp_timer_countdown = next > 0 ? next - 1 : 0;

  if (timer_on)
    return;

  timer_on = 1;
  signal(SIGTIMR, timer_action);
  __dpmi_get_protected_mode_interrupt_vector(8, &__djgpp_old_timer);
  int8.selector = _my_cs();
  int8.offset32 = (unsigned) &__djgpp_timer_hdlr;
  __dpmi_set_protected_mode_interrupt_vector(8, &int8);
}


int
setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
{
  uclock_t *t_exp, *t_rel;

  if (ovalue)
  {
    if (getitimer(which,ovalue)) /* also sets u_now */
      return -1;  /* errno already set */
  }
  else
    u_now = uclock();

  if ((which != ITIMER_REAL) && ( which != ITIMER_PROF ) )
  {
    errno = EINVAL;
    return -1;
  }

  t_exp = which == ITIMER_REAL ? &r_exp: &p_exp;
  t_rel = which == ITIMER_REAL ? &r_rel: &p_rel;

  if ((value->it_value.tv_sec|value->it_value.tv_usec)==0 )
  {
    /* Disable this timer */
    *t_exp = *t_rel = 0;
    /* If both stopped, stop timer */
    if (( p_exp | r_exp ) == 0 )
    {
      stop_timer();
      return 0;
    }
  }

  *t_exp = value->it_value.tv_sec    * UCLOCKS_PER_SEC;
  *t_rel = value->it_interval.tv_sec * UCLOCKS_PER_SEC;

  /* Rounding errors ?? First multiply and then divide gives an
     overflow if the USEC member is larger than 524288. */
  if (value->it_value.tv_usec < 524200)
    *t_exp += (value->it_value.tv_usec * 4096) / 3433;
  else
    *t_exp += (value->it_value.tv_usec * 2048) / 1716;

  if (value->it_interval.tv_usec < 524200)
    *t_rel += (value->it_interval.tv_usec * 4096) / 3433;
  else
    *t_rel += (value->it_interval.tv_usec * 2048) / 1716;

  /* u_now is returned zero first time uclock() is called.  That first
     call could be the one we issued above, or it could be two days
     ago, when the calling program started.  We need to make {rp}_exp
     and u_now be relative to the same point of origin.  */
  *t_exp += u_now;

  start_timer();
  return 0;
}