[parisc-linux] [PATCH] timer_interrupt and gettimeoffset.
Grant Grundler
grundler at parisc-linux.org
Fri Sep 1 16:48:25 MDT 2006
On Thu, Aug 31, 2006 at 12:53:27AM -0600, Grant Grundler wrote:
> And I've hacked your version some more.
> diff is below.
version #3: seems to be working fine on 64-bit SMP.
32-bit UP kernel is still under construction.
That means gettimeoffset() hasn't been tested.
And I'm getting the following warnings on my b2600:
...
Setting the system clock..
timer_interrupt(CPU 0): delayed! run ntpdate ticks 859 cycles FFF51A1C rem 40E59C next/now FFFE7A9D/96080
gettimeoffset(CPU -119762782): missing ticks!cycles FFC87AE4 prev/now/next 6EBEA41/14C624/4C4B40 clock 0
gettimeoffset(CPU -177625053): missing ticks!cycles FFC87AE4 prev/now/next A5ED2C0/14C624/4C4B40 clock 12
gettimeoffset(CPU -238800592): missing ticks!cycles FFC87AE4 prev/now/next E0449B3/14C624/4C4B40 clock 12
gettimeoffset(CPU -302979574): missing ticks!cycles FFC87AE4 prev/now/next 11D794D9/14C624/4C4B40 clock 0
Sysgettimeoffset(CPU -361861366): missing ticks!cycles FFC87AE4 prev/now/next 155A0BD9/14C624/4C4B40 clock 12
tem Clock set. Local time: Fri Sep 1 22:42:09 UTC 2006.
gettimeoffset printk is busticated. I'll fix that in the next version.
But it looks like wrapped values are causing problems.
The timer_interrupt warning might be reasonable given we are making
a call to firmware to set the clock and block interrupts for
the duration.
In addition to time.c, two more files are touched:
smp.c I couldn't see where slave CPUs would start
the interval timer and added the call here.
param.h Use CONFIG_HZ for interval timer.
We were ignored this before.
I just realized one small change to arch/parisc/kernel/processor.c
is missin from this diff. We don't want processor_probe() to clobber
CPU0's cpu_data. "it_value" has already been initialized.
enjoy!
grant
diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
index 98e4095..f33e8de 100644
--- a/arch/parisc/kernel/smp.c
+++ b/arch/parisc/kernel/smp.c
@@ -430,8 +430,9 @@ smp_do_timer(struct pt_regs *regs)
static void __init
smp_cpu_init(int cpunum)
{
- extern int init_per_cpu(int); /* arch/parisc/kernel/setup.c */
+ extern int init_per_cpu(int); /* arch/parisc/kernel/processor.c */
extern void init_IRQ(void); /* arch/parisc/kernel/irq.c */
+ extern void start_cpu_itimer(void); /* arch/parisc/kernel/time.c */
/* Set modes and Enable floating point coprocessor */
(void) init_per_cpu(cpunum);
@@ -457,6 +458,7 @@ smp_cpu_init(int cpunum)
enter_lazy_tlb(&init_mm, current);
init_IRQ(); /* make sure no IRQ's are enabled or pending */
+ start_cpu_itimer();
}
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c
index 5facc9b..337c4ec 100644
--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -35,8 +35,8 @@ #include <linux/timex.h>
/* xtime and wall_jiffies keep wall-clock time */
extern unsigned long wall_jiffies;
-static long clocktick __read_mostly; /* timer cycles per tick */
-static long halftick __read_mostly;
+static unsigned long clocktick __read_mostly; /* timer cycles per tick */
+static unsigned long halftick __read_mostly;
#ifdef CONFIG_SMP
extern void smp_do_timer(struct pt_regs *regs);
@@ -44,34 +44,77 @@ #endif
irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
- long now;
- long next_tick;
- int nticks;
+ unsigned long now;
+ unsigned long next_tick;
+ unsigned long cycles_elapsed;
+ unsigned long cycles_remainder;
+ unsigned long ticks_elapsed = 1; /* at least one elapsed */
int cpu = smp_processor_id();
profile_tick(CPU_PROFILING, regs);
- now = mfctl(16);
- /* initialize next_tick to time at last clocktick */
+ /* Initialize next_tick to the expected tick time. */
next_tick = cpu_data[cpu].it_value;
- /* since time passes between the interrupt and the mfctl()
- * above, it is never true that last_tick + clocktick == now. If we
- * never miss a clocktick, we could set next_tick = last_tick + clocktick
- * but maybe we'll miss ticks, hence the loop.
- *
- * Variables are *signed*.
+ /* Get current interval timer.
+ * CR16 reads as 64 bits in CPU wide mode.
+ * CR16 reads as 32 bits in CPU narrow mode.
*/
+ now = mfctl(16);
+
+ cycles_elapsed = now - next_tick;
+
+ /* Determine how much time elapsed. */
+ if (now < next_tick) {
+ /* Scenario 2: CR16 wrapped after clock tick.
+ * 1's complement will give us the "elapse cycles".
+ *
+ * This "cr16 wrapped" cruft is primarily for 32-bit kernels.
+ * So think "unsigned long is u32" when reading the code.
+ * And yes, of course 64-bit will someday wrap, but only
+ * every 198841 days on a 1GHz machine.
+ */
+ cycles_elapsed = ~cycles_elapsed; /* off by one cycle - don't care */
+ }
+
+ ticks_elapsed += cycles_elapsed / clocktick;
+ cycles_remainder = cycles_elapsed % clocktick;
- nticks = 0;
- while((next_tick - now) < halftick) {
- next_tick += clocktick;
- nticks++;
+ /* Can we differentiate between "early CR16" (aka Scenario 1) and
+ * "long delay" (aka Scenario 3)? I don't think so.
+ *
+ * We expected timer_interrupt to be delivered at least a few hundred
+ * cycles after the IT fires. But it's arbitrary how much time passes
+ * before we call it "late". I've picked one second.
+ */
+ if (ticks_elapsed > HZ) {
+ /* Scenario 3: very long delay? bad in any case */
+ printk (KERN_CRIT "timer_interrupt(CPU %d): delayed! run ntpdate"
+ " ticks %ld cycles %lX rem %lX"
+ " next/now %lX/%lX\n",
+ cpu,
+ ticks_elapsed, cycles_elapsed, cycles_remainder,
+ next_tick, now );
+
+ ticks_elapsed = 1; /* hack to limit damage in loop below */
}
+
+
+ /* Determine when (in CR16 cycles) next IT interrupt will fire.
+ * We want IT to fire modulo clocktick even if we miss/skip some.
+ * But those interrupts don't in fact get delivered that regularly.
+ */
+ next_tick = now + (clocktick - cycles_remainder);
+
+ /* Program the IT when to deliver the next interrupt. */
+ /* Only bottom 32-bits of next_tick are written to cr16. */
mtctl(next_tick, 16);
cpu_data[cpu].it_value = next_tick;
- while (nticks--) {
+ /* Now that we are done mucking with unreliable delivery of interrupts,
+ * go do system house keeping.
+ */
+ while (ticks_elapsed--) {
#ifdef CONFIG_SMP
smp_do_timer(regs);
#else
@@ -124,21 +167,40 @@ #ifndef CONFIG_SMP
* Once parisc-linux learns the cr16 difference between processors,
* this could be made to work.
*/
- long last_tick;
- long elapsed_cycles;
+ unsigned long now;
+ unsigned long prev_tick;
+ unsigned long next_tick;
+ unsigned long elapsed_cycles;
+ unsigned long usec;
- /* it_value is the intended time of the next tick */
- last_tick = cpu_data[smp_processor_id()].it_value;
+ next_tick = cpu_data[smp_processor_id()].it_value;
+ now = mfctl(16); /* Read the hardware interval timer. */
- /* Subtract one tick and account for possible difference between
- * when we expected the tick and when it actually arrived.
- * (aka wall vs real)
- */
- last_tick -= clocktick * (jiffies - wall_jiffies + 1);
- elapsed_cycles = mfctl(16) - last_tick;
+ prev_tick = next_tick - clocktick;
- /* the precision of this math could be improved */
- return elapsed_cycles / (PAGE0->mem_10msec / 10000);
+ /* Assume Scenario 1: "now" is later than prev_tick. */
+ elapsed_cycles = now - prev_tick;
+
+ if (now < prev_tick) {
+ /* Scenario 2: CR16 wrapped!
+ * 1's complement is close enough.
+ */
+ elapsed_cycles = ~elapsed_cycles;
+ }
+
+ if (elapsed_cycles > (HZ * clocktick)) {
+ /* Scenario 3: clock ticks are missing. */
+ printk (KERN_CRIT "gettimeoffset(CPU %d): missing ticks!"
+ "cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n",
+ elapsed_cycles, prev_tick, now, next_tick, clocktick);
+ }
+
+ /* FIXME: Can we improve the precision? Not with PAGE0. */
+ usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
+
+ /* add in "lost" jiffies */
+ usec += clocktick * (jiffies - wall_jiffies);
+ return usec;
#else
return 0;
#endif
@@ -149,6 +211,7 @@ do_gettimeofday (struct timeval *tv)
{
unsigned long flags, seq, usec, sec;
+ /* Hold xtime_lock and adjust timeval. */
do {
seq = read_seqbegin_irqsave(&xtime_lock, flags);
usec = gettimeoffset();
@@ -156,25 +219,13 @@ do_gettimeofday (struct timeval *tv)
usec += (xtime.tv_nsec / 1000);
} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
- if (unlikely(usec > LONG_MAX)) {
- /* This can happen if the gettimeoffset adjustment is
- * negative and xtime.tv_nsec is smaller than the
- * adjustment */
- printk(KERN_ERR "do_gettimeofday() spurious xtime.tv_nsec of %ld\n", usec);
- usec += USEC_PER_SEC;
- --sec;
- /* This should never happen, it means the negative
- * time adjustment was more than a second, so there's
- * something seriously wrong */
- BUG_ON(usec > LONG_MAX);
- }
-
-
+ /* Move adjusted usec's into sec's. */
while (usec >= USEC_PER_SEC) {
usec -= USEC_PER_SEC;
++sec;
}
+ /* Return adjusted result. */
tv->tv_sec = sec;
tv->tv_usec = usec;
}
@@ -226,22 +277,24 @@ unsigned long long sched_clock(void)
}
+void __init start_cpu_itimer(void)
+{
+ unsigned int cpu = smp_processor_id();
+ unsigned long next_tick = mfctl(16) + clocktick;
+
+ mtctl(next_tick, 16); /* kick off Interval Timer (CR16) */
+
+ cpu_data[cpu].it_value = next_tick;
+}
+
void __init time_init(void)
{
- unsigned long next_tick;
static struct pdc_tod tod_data;
clocktick = (100 * PAGE0->mem_10msec) / HZ;
halftick = clocktick / 2;
- /* Setup clock interrupt timing */
-
- next_tick = mfctl(16);
- next_tick += clocktick;
- cpu_data[smp_processor_id()].it_value = next_tick;
-
- /* kick off Itimer (CR16) */
- mtctl(next_tick, 16);
+ start_cpu_itimer(); /* get CPU 0 started */
if(pdc_tod_read(&tod_data) == 0) {
write_seqlock_irq(&xtime_lock);
diff --git a/include/asm-parisc/param.h b/include/asm-parisc/param.h
index 07cb9b9..32e03d8 100644
--- a/include/asm-parisc/param.h
+++ b/include/asm-parisc/param.h
@@ -2,13 +2,9 @@ #ifndef _ASMPARISC_PARAM_H
#define _ASMPARISC_PARAM_H
#ifdef __KERNEL__
-# ifdef CONFIG_PA20
-# define HZ 1000 /* Faster machines */
-# else
-# define HZ 100 /* Internal kernel timer frequency */
-# endif
-# define USER_HZ 100 /* .. some user interfaces are in "ticks" */
-# define CLOCKS_PER_SEC (USER_HZ) /* like times() */
+#define HZ CONFIG_HZ
+#define USER_HZ 100 /* some user API use "ticks" */
+#define CLOCKS_PER_SEC (USER_HZ) /* like times() */
#endif
#ifndef HZ
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