In trying the latest development kernel, I've noticed that calling
setitimer with a 1 usec delay (the shortest possible delay) results in
the timer never going off. 2 usec is ok but 1 is not, so I suspect
that somehow things are being rounded off incorrectly. The attached
program demonstrates the problem on 2.5.69, but runs correctly on a
2.4.20 kernel.
I have only had the opportunity to try this on a single architecture
(ia64), so if anyone can convince me that it's a platform-specific
problem I'll be happy to take my gripe to the ia64 list. I've tried to
figure out how the usecs are converted to jiffies, but the code is
sufficiently convoluted that I thought I'd throw it out in the hope of
finding someone who understands the situation a little better.
- Richard
// When run, this program should print "handled alarm" from within the
// signal handler, and "out of sigsuspend" right after. It works on
// 2.4.20 or if MY_TIMER_USEC is >= 2, but not on 2.5.69 with
// MY_TIMER_USEC = 1.
#define MY_TIMER_USEC 1
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>
void
alarm_handler( int x )
{
printf( "handled alarm\n" );
return;
}
int
main()
{
struct itimerval it = { { 0, 0 }, { 0, MY_TIMER_USEC } };
sigset_t mask;
struct sigaction act;
act.sa_handler = alarm_handler;
act.sa_flags = 0;
sigemptyset( &act.sa_mask );
if( sigaction(SIGALRM, &act, 0) ) {
perror( "sigaction" );
exit( 1 );
}
if( setitimer(ITIMER_REAL, &it, 0) ) {
perror( "setitimer" );
exit( 1 );
}
sigemptyset( &mask );
sigsuspend( &mask );
printf( "out of sigsuspend\n" );
return 0;
}
--
Richard C. Bilson, Research Assistant | School of Computer Science
[email protected] | University of Waterloo
http://plg.uwaterloo.ca/~rcbilson | 200 University Avenue West
Office: DC 3548F Ph: (519)888-4567x4822 | Waterloo, Ontario, CANADA N2L 3G1
diff -urN -X /home/piele/dontdiff linux-2.5.69-ia64-030521.orig/Makefile linux-2.5.69-ia64-sleep/Makefile
--- linux-2.5.69-ia64-030521.orig/Makefile 2003-05-26 12:03:13.000000000 +0200
+++ linux-2.5.69-ia64-sleep/Makefile 2003-05-26 14:16:25.000000000 +0200
@@ -1,7 +1,7 @@
VERSION = 2
PATCHLEVEL = 5
SUBLEVEL = 69
-EXTRAVERSION = -eric-2
+EXTRAVERSION = -eric-sleep-2
# *DOCUMENTATION*
# To see a list of typical targets execute "make help"
Binary files linux-2.5.69-ia64-030521.orig/arch/ia64/boot/vmlinux.gz and linux-2.5.69-ia64-sleep/arch/ia64/boot/vmlinux.gz differ
diff -urN -X /home/piele/dontdiff linux-2.5.69-ia64-030521.orig/fs/proc/proc_misc.c linux-2.5.69-ia64-sleep/fs/proc/proc_misc.c
--- linux-2.5.69-ia64-030521.orig/fs/proc/proc_misc.c 2003-05-05 01:53:02.000000000 +0200
+++ linux-2.5.69-ia64-sleep/fs/proc/proc_misc.c 2003-05-26 13:00:47.000000000 +0200
@@ -137,36 +137,20 @@
static int uptime_read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
- u64 uptime;
- unsigned long uptime_remainder;
+ u64 uptime, idle = init_task.utime + init_task.stime;
+ unsigned long uptime_remainder, idle_remainder;
int len;
uptime = get_jiffies_64() - INITIAL_JIFFIES;
uptime_remainder = (unsigned long) do_div(uptime, HZ);
+ idle_remainder = (unsigned long) do_div(idle, HZ);
-#if HZ!=100
- {
- u64 idle = init_task.utime + init_task.stime;
- unsigned long idle_remainder;
-
- idle_remainder = (unsigned long) do_div(idle, HZ);
- len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
- (unsigned long) uptime,
- (uptime_remainder * 100) / HZ,
- (unsigned long) idle,
- (idle_remainder * 100) / HZ);
- }
-#else
- {
- unsigned long idle = init_task.utime + init_task.stime;
-
- len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
- (unsigned long) uptime,
- uptime_remainder,
- idle / HZ,
- idle % HZ);
- }
-#endif
+ len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
+ (unsigned long) uptime,
+ (uptime_remainder * 100) / HZ,
+ (unsigned long) idle,
+ (idle_remainder * 100) / HZ);
+
return proc_calc_metrics(page, start, off, count, eof, len);
}
diff -urN -X /home/piele/dontdiff linux-2.5.69-ia64-030521.orig/include/linux/timex.h linux-2.5.69-ia64-sleep/include/linux/timex.h
--- linux-2.5.69-ia64-030521.orig/include/linux/timex.h 2003-05-26 11:01:49.000000000 +0200
+++ linux-2.5.69-ia64-sleep/include/linux/timex.h 2003-05-26 13:00:47.000000000 +0200
@@ -157,27 +157,12 @@
/* LATCH is used in the interval timer and ftape setup. */
#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */
-/* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the we can
- * improve accuracy by shifting LSH bits, hence calculating:
- * (NOM << LSH) / DEN
- * This however means trouble for large NOM, because (NOM << LSH) may no
- * longer fit in 32 bits. The following way of calculating this gives us
- * some slack, under the following onditions:
- * - (NOM / DEN) fits in (32 - LSH) bits.
- * - (NOM % DEN) fits in (32 - LSH) bits.
- */
-#define SH_DIV(NOM,DEN,LSH) ( ((NOM / DEN) << LSH) \
- + (((NOM % DEN) << LSH) + DEN / 2) / DEN)
-
-/* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
-#define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
-
/* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
-#define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
+#define TICK_USEC ((TICK_NSEC(TUSEC) + 1000UL/2) / 1000UL)
/* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ and */
/* a value TUSEC for TICK_USEC (can be set bij adjtimex) */
-#define TICK_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8))
+#define TICK_NSEC(TUSEC) ((1000000000UL + USER_HZ/2) / USER_HZ)
#include <linux/time.h>
/*
diff -urN -X /home/piele/dontdiff linux-2.5.69-ia64-030521.orig/kernel/posix-timers.c linux-2.5.69-ia64-sleep/kernel/posix-timers.c
--- linux-2.5.69-ia64-030521.orig/kernel/posix-timers.c 2003-05-26 11:01:49.000000000 +0200
+++ linux-2.5.69-ia64-sleep/kernel/posix-timers.c 2003-05-26 15:37:34.000000000 +0200
@@ -1210,8 +1210,8 @@
if (abs || !rq_time) {
adjust_abs_time(&posix_clocks[which_clock], &t, abs,
&rq_time);
+ rq_time += (t.tv_sec || t.tv_nsec);
}
-
left = rq_time - get_jiffies_64();
if (left >= (s64)MAX_JIFFY_OFFSET)
left = (s64)MAX_JIFFY_OFFSET;
diff -urN -X /home/piele/dontdiff linux-2.5.69-ia64-030521.orig/kernel/timer.c linux-2.5.69-ia64-sleep/kernel/timer.c
--- linux-2.5.69-ia64-030521.orig/kernel/timer.c 2003-05-26 11:01:50.000000000 +0200
+++ linux-2.5.69-ia64-sleep/kernel/timer.c 2003-05-26 13:00:47.000000000 +0200
@@ -469,7 +469,7 @@
long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
long time_phase; /* phase offset (scaled us) */
-long time_freq = ((1000000 + HZ/2) % HZ - HZ/2) << SHIFT_USEC;
+long time_freq = (((NSEC_PER_SEC + HZ/2) % HZ - HZ/2) << SHIFT_USEC) / NSEC_PER_USEC;
/* frequency offset (scaled ppm)*/
long time_adj; /* tick adjust (scaled 1 / HZ) */
long time_reftime; /* time at last adjustment (s) */
@@ -633,12 +633,12 @@
* advance the tick more.
*/
time_phase += time_adj;
- if (time_phase <= -FINEUSEC) {
- long ltemp = -time_phase >> (SHIFT_SCALE - 10);
+ if (time_phase <= -(FINEUSEC >> 10)) {
+ long ltemp = -time_phase >> (SHIFT_SCALE - 10); /* quick fix for nsec : 2^10 ~ 1000 */
time_phase += ltemp << (SHIFT_SCALE - 10);
delta_nsec -= ltemp;
}
- else if (time_phase >= FINEUSEC) {
+ else if (time_phase >= (FINEUSEC >> 10)) {
long ltemp = time_phase >> (SHIFT_SCALE - 10);
time_phase -= ltemp << (SHIFT_SCALE - 10);
delta_nsec += ltemp;
Binary files linux-2.5.69-ia64-030521.orig/scripts/kconfig/conf and linux-2.5.69-ia64-sleep/scripts/kconfig/conf differ
Binary files linux-2.5.69-ia64-030521.orig/vmlinux.gz and linux-2.5.69-ia64-sleep/vmlinux.gz differ
> From [email protected] Tue May 27 05:05:53 2003
>
> With the patch atatched the bug seems to go away, for the 030521 release
> of IA64 patch (and probably the previous release also). Could you
> confirm, Richard? I think it's kind of architecture specific because
> this bug shouldn't happen with HZ=1000 (i386) ;-)
Yes -- it fixes the program I posted, as well as my original program.
Thanks very much, Eric!
- Richard