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Subject[RFC][PATCH] linux-2.5.64_monotonic-clock_A0
From
Date
All,
Recently I've been working with Joel Becker, author of the
hangcheck-timer code (already accepted into 2.5) to resolve issues when
running his code on systems without synced TSCs.

The basic problem is that the hangcheck-timer code (Required for Oracle)
needs a accurate hard clock which can be used to detect OS stalls (due
to udelay() or pci bus hangs) that would cause system time to skew (its
sort of a sanity check that insures the system's notion of time is
accurate). However, currently they are using get_cycles() to fetch the
cpu's TSC register, thus this does not work on systems w/o a synced TSC.
As suggested by Andi Kleen (see thread here:
http://www.uwsg.iu.edu/hypermail/linux/kernel/0302.0/1234.html ) I've
worked with Joel and others to implement the monotonic_clock()
interface.

This interface returns a unsigned long long representing the number of
nanoseconds that has passed since time_init().

Since we're dealing with 64bit values the cost of the math required to
do the cycles->ns conversion is a big concern. I'd be very happy if
someone could suggest a faster way.

Future plans to the interface include properly handling cpu_freq changes
and porting to the different arches.

Comments and suggestions requested, flames expected :)

thanks
-john

diff -Nru a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
--- a/arch/i386/kernel/time.c Thu Mar 6 16:12:27 2003
+++ b/arch/i386/kernel/time.c Thu Mar 6 16:12:27 2003
@@ -138,6 +138,19 @@
clock_was_set();
}

+unsigned long long monotonic_clock(void)
+{
+ unsigned long long ret;
+ unsigned long seq;
+ do {
+ seq = read_seqbegin(&xtime_lock);
+ ret = timer->monotonic_clock();
+ } while (read_seqretry(&xtime_lock, seq));
+ return ret;
+}
+EXPORT_SYMBOL(monotonic_clock);
+
+
/*
* In order to set the CMOS clock precisely, set_rtc_mmss has to be
* called 500 ms after the second nowtime has started, because when
diff -Nru a/arch/i386/kernel/timers/timer_cyclone.c b/arch/i386/kernel/timers/timer_cyclone.c
--- a/arch/i386/kernel/timers/timer_cyclone.c Thu Mar 6 16:12:27 2003
+++ b/arch/i386/kernel/timers/timer_cyclone.c Thu Mar 6 16:12:27 2003
@@ -27,19 +27,24 @@
#define CYCLONE_MPMC_OFFSET 0x51D0
#define CYCLONE_MPCS_OFFSET 0x51A8
#define CYCLONE_TIMER_FREQ 100000000
-
+#define CYCLONE_TIMER_MASK (((u64)1<<40)-1) /*40 bit mask*/
int use_cyclone = 0;

static u32* volatile cyclone_timer; /* Cyclone MPMC0 register */
-static u32 last_cyclone_timer;
+static u32 last_cyclone_low;
+static u32 last_cyclone_high;
+static unsigned long long monotonic_base;

static void mark_offset_cyclone(void)
{
int count;
+ unsigned long long this_offset, last_offset;
+ last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
+
spin_lock(&i8253_lock);
/* quickly read the cyclone timer */
- if(cyclone_timer)
- last_cyclone_timer = cyclone_timer[0];
+ last_cyclone_high = cyclone_timer[1];
+ last_cyclone_low = cyclone_timer[0];

/* calculate delay_at_last_interrupt */
outb_p(0x00, 0x43); /* latch the count ASAP */
@@ -50,6 +55,10 @@

count = ((LATCH-1) - count) * TICK_SIZE;
delay_at_last_interrupt = (count + LATCH/2) / LATCH;
+
+ /* update the monotonic base value */
+ this_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
+ monotonic_base += (this_offset - last_offset) & CYCLONE_TIMER_MASK;
}

static unsigned long get_offset_cyclone(void)
@@ -63,7 +72,7 @@
offset = cyclone_timer[0];

/* .. relative to previous jiffy */
- offset = offset - last_cyclone_timer;
+ offset = offset - last_cyclone_low;

/* convert cyclone ticks to microseconds */
/* XXX slow, can we speed this up? */
@@ -73,6 +82,21 @@
return delay_at_last_interrupt + offset;
}

+static unsigned long long monotonic_clock_cyclone(void)
+{
+
+ u32 now_low = cyclone_timer[0];
+ u32 now_high = cyclone_timer[1];
+ unsigned long long last_offset, this_offset;
+ unsigned long long ret;
+ last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
+ this_offset = ((unsigned long long)now_high<<32)|now_low;
+
+ ret = monotonic_base + ((this_offset - last_offset)&CYCLONE_TIMER_MASK);
+ ret = ret * (1000000000 / CYCLONE_TIMER_FREQ);
+ return ret;
+}
+
static int init_cyclone(void)
{
u32* reg;
@@ -190,5 +214,6 @@
.init = init_cyclone,
.mark_offset = mark_offset_cyclone,
.get_offset = get_offset_cyclone,
+ .monotonic_clock = monotonic_clock_cyclone,
.delay = delay_cyclone,
};
diff -Nru a/arch/i386/kernel/timers/timer_none.c b/arch/i386/kernel/timers/timer_none.c
--- a/arch/i386/kernel/timers/timer_none.c Thu Mar 6 16:12:27 2003
+++ b/arch/i386/kernel/timers/timer_none.c Thu Mar 6 16:12:27 2003
@@ -15,6 +15,11 @@
return 0;
}

+static unsigned long long monotonic_clock_none(void)
+{
+ return 0;
+}
+
static void delay_none(unsigned long loops)
{
int d0;
@@ -33,5 +38,6 @@
.init = init_none,
.mark_offset = mark_offset_none,
.get_offset = get_offset_none,
+ .monotonic_clock = monotonic_clock_none,
.delay = delay_none,
};
diff -Nru a/arch/i386/kernel/timers/timer_pit.c b/arch/i386/kernel/timers/timer_pit.c
--- a/arch/i386/kernel/timers/timer_pit.c Thu Mar 6 16:12:27 2003
+++ b/arch/i386/kernel/timers/timer_pit.c Thu Mar 6 16:12:27 2003
@@ -27,6 +27,11 @@
/* nothing needed */
}

+static unsigned long long monotonic_clock_pit(void)
+{
+ return 0;
+}
+
static void delay_pit(unsigned long loops)
{
int d0;
@@ -141,5 +146,6 @@
.init = init_pit,
.mark_offset = mark_offset_pit,
.get_offset = get_offset_pit,
+ .monotonic_clock = monotonic_clock_pit,
.delay = delay_pit,
};
diff -Nru a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
--- a/arch/i386/kernel/timers/timer_tsc.c Thu Mar 6 16:12:27 2003
+++ b/arch/i386/kernel/timers/timer_tsc.c Thu Mar 6 16:12:27 2003
@@ -23,6 +23,45 @@
static int delay_at_last_interrupt;

static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
+static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
+static unsigned long long monotonic_base;
+
+
+/*
+ * accurate 64-bit/32-bit division, stolen from smpboot.c
+ */
+unsigned long long div64 (unsigned long long a, unsigned long b0)
+{
+ unsigned int a1, a2;
+ unsigned long long res;
+
+ a1 = ((unsigned int*)&a)[0];
+ a2 = ((unsigned int*)&a)[1];
+
+ res = a1/b0 +
+ (unsigned long long)a2 * (unsigned long long)(0xffffffff/b0) +
+ a2 / b0 +
+ (a2 * (0xffffffff % b0)) / b0;
+
+ return res;
+}
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+ unsigned long long ret;
+ unsigned long cpu_mhz = cpu_khz/1000;
+
+ /* convert from cycles(64bits) => nanoseconds (64bits)
+ * basic equation:
+ * cycles / ((cycles / sec) * (1sec / 10^9ns)) = ns
+ * cycles / ((cpu_mhz * 1000000) / 10^9)) = ns
+ * cycles / (cpu_mhz / 10^3) = ns
+ * cycles * 10^3 / cpu_mhz = ns
+ */
+ ret = cyc * 1000;
+ ret = div64(ret,cpu_mhz);
+ return ret;
+}

/* Cached *multiplier* to convert TSC counts to microseconds.
* (see the equation below).
@@ -60,11 +99,25 @@
return delay_at_last_interrupt + edx;
}

+static unsigned long long monotonic_clock_tsc(void)
+{
+ unsigned long long last_offset, this_offset;
+ last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
+
+ /* Read the Time Stamp Counter */
+ rdtscll(this_offset);
+
+ /* return the value in ns */
+ return monotonic_base + cycles_2_ns(this_offset - last_offset);
+}
+
static void mark_offset_tsc(void)
{
int count;
int countmp;
static int count1=0, count2=LATCH;
+ unsigned long long this_offset, last_offset;
+ last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
/*
* It is important that these two operations happen almost at
* the same time. We do the RDTSC stuff first, since it's
@@ -79,7 +132,7 @@

/* read Pentium cycle counter */

- rdtscl(last_tsc_low);
+ rdtsc(last_tsc_low, last_tsc_high);

spin_lock(&i8253_lock);
outb_p(0x00, 0x43); /* latch the count ASAP */
@@ -104,6 +157,11 @@

count = ((LATCH-1) - count) * TICK_SIZE;
delay_at_last_interrupt = (count + LATCH/2) / LATCH;
+
+ /* update the monotonic base value */
+ this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
+ monotonic_base += cycles_2_ns(this_offset - last_offset);
+
}

static void delay_tsc(unsigned long loops)
@@ -326,5 +384,6 @@
.init = init_tsc,
.mark_offset = mark_offset_tsc,
.get_offset = get_offset_tsc,
+ .monotonic_clock = monotonic_clock_tsc,
.delay = delay_tsc,
};
diff -Nru a/drivers/char/hangcheck-timer.c b/drivers/char/hangcheck-timer.c
--- a/drivers/char/hangcheck-timer.c Thu Mar 6 16:12:27 2003
+++ b/drivers/char/hangcheck-timer.c Thu Mar 6 16:12:27 2003
@@ -78,11 +78,13 @@
static struct timer_list hangcheck_ticktock =
TIMER_INITIALIZER(hangcheck_fire, 0, 0);

+extern unsigned long long monotonic_clock(void);
+
static void hangcheck_fire(unsigned long data)
{
unsigned long long cur_tsc, tsc_diff;

- cur_tsc = get_cycles();
+ cur_tsc = monotonic_clock();

if (cur_tsc > hangcheck_tsc)
tsc_diff = cur_tsc - hangcheck_tsc;
@@ -98,7 +100,7 @@
}
}
mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
- hangcheck_tsc = get_cycles();
+ hangcheck_tsc = monotonic_clock();
}


@@ -108,10 +110,10 @@
VERSION_STR, hangcheck_tick, hangcheck_margin);

hangcheck_tsc_margin = hangcheck_margin + hangcheck_tick;
- hangcheck_tsc_margin *= HZ;
- hangcheck_tsc_margin *= current_cpu_data.loops_per_jiffy;
+ hangcheck_tsc_margin *= 1000000000;
+

- hangcheck_tsc = get_cycles();
+ hangcheck_tsc = monotonic_clock();
mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));

return 0;
diff -Nru a/include/asm-i386/timer.h b/include/asm-i386/timer.h
--- a/include/asm-i386/timer.h Thu Mar 6 16:12:27 2003
+++ b/include/asm-i386/timer.h Thu Mar 6 16:12:27 2003
@@ -14,6 +14,7 @@
int (*init)(void);
void (*mark_offset)(void);
unsigned long (*get_offset)(void);
+ unsigned long long (*monotonic_clock)(void);
void (*delay)(unsigned long);
};


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