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All,=20
Here is the next rev of my monotonic-clock patch. Adds fixes to
insure atomicity when reading the cyclone register, as well as minor
cleanups to the scaled math code. I plan on submitting this later this
week if no major complaints are raised.=20
This patch, written with the advice of Joel Becker, addresses a
problem with the hangcheck-timer. 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. Some of the major considerations made when writing this patch
were:=20
o Needs to be able to return accurate time in the absence of
multiple timer interrupts
o Needs to be abstracted out from the hardware
o Avoids impacting gettimeofday() performance
This interface returns a unsigned long long representing the number of
nanoseconds that has passed since time_init().=20
Future plans to the interface include properly handling cpu_freq changes
and porting to the different arches.
Comments, suggestions and flames welcome.
thanks
-john
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diff -Nru a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
--- a/arch/i386/kernel/time.c Tue Mar 25 15:48:49 2003
+++ b/arch/i386/kernel/time.c Tue Mar 25 15:48:49 2003
@@ -138,6 +138,19 @@
clock_was_set();
}
=20
+unsigned long long monotonic_clock(void)
+{
+ unsigned long long ret;
+ unsigned long seq;
+ do {
+ seq =3D read_seqbegin(&xtime_lock);
+ ret =3D 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/time=
rs/timer_cyclone.c
--- a/arch/i386/kernel/timers/timer_cyclone.c Tue Mar 25 15:48:49 2003
+++ b/arch/i386/kernel/timers/timer_cyclone.c Tue Mar 25 15:48:49 2003
@@ -27,19 +27,26 @@
#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 =3D 0;
=20
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;
=20
static void mark_offset_cyclone(void)
{
int count;
+ unsigned long long this_offset, last_offset;
+ last_offset =3D ((unsigned long long)last_cyclone_high<<32)|last_cyclone_=
low;
+=09
spin_lock(&i8253_lock);
/* quickly read the cyclone timer */
- if(cyclone_timer)
- last_cyclone_timer =3D cyclone_timer[0];
+ do {=09
+ last_cyclone_high =3D cyclone_timer[1];
+ last_cyclone_low =3D cyclone_timer[0];
+ } while (last_cyclone_high !=3D cyclone_timer[1]);
=20
/* calculate delay_at_last_interrupt */
outb_p(0x00, 0x43); /* latch the count ASAP */
@@ -50,6 +57,10 @@
=20
count =3D ((LATCH-1) - count) * TICK_SIZE;
delay_at_last_interrupt =3D (count + LATCH/2) / LATCH;
+
+ /* update the monotonic base value */
+ this_offset =3D ((unsigned long long)last_cyclone_high<<32)|last_cyclone_=
low;
+ monotonic_base +=3D (this_offset - last_offset) & CYCLONE_TIMER_MASK;
}
=20
static unsigned long get_offset_cyclone(void)
@@ -63,7 +74,7 @@
offset =3D cyclone_timer[0];
=20
/* .. relative to previous jiffy */
- offset =3D offset - last_cyclone_timer;
+ offset =3D offset - last_cyclone_low;
=20
/* convert cyclone ticks to microseconds */=09
/* XXX slow, can we speed this up? */
@@ -73,6 +84,25 @@
return delay_at_last_interrupt + offset;
}
=20
+static unsigned long long monotonic_clock_cyclone(void)
+{
+=09
+ u32 now_low, now_high;
+ unsigned long long last_offset, this_offset;
+ unsigned long long ret;
+
+ do {
+ now_high =3D cyclone_timer[1];
+ now_low =3D cyclone_timer[0];
+ } while (now_high !=3D cyclone_timer[1]);
+ last_offset =3D ((unsigned long long)last_cyclone_high<<32)|last_cyclone_=
low;
+ this_offset =3D ((unsigned long long)now_high<<32)|now_low;
+=09
+ ret =3D monotonic_base + ((this_offset - last_offset)&CYCLONE_TIMER_MASK)=
;
+ ret =3D ret * (1000000000 / CYCLONE_TIMER_FREQ);
+ return ret;
+}
+
static int init_cyclone(void)
{
u32* reg;=09
@@ -190,5 +220,6 @@
.init =3D init_cyclone,=20
.mark_offset =3D mark_offset_cyclone,=20
.get_offset =3D get_offset_cyclone,
+ .monotonic_clock =3D monotonic_clock_cyclone,
.delay =3D 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 Tue Mar 25 15:48:49 2003
+++ b/arch/i386/kernel/timers/timer_none.c Tue Mar 25 15:48:49 2003
@@ -15,6 +15,11 @@
return 0;
}
=20
+static unsigned long long monotonic_clock_none(void)
+{
+ return 0;
+}
+
static void delay_none(unsigned long loops)
{
int d0;
@@ -33,5 +38,6 @@
.init =3D init_none,=20
.mark_offset =3D mark_offset_none,=20
.get_offset =3D get_offset_none,
+ .monotonic_clock =3D monotonic_clock_none,
.delay =3D delay_none,
};
diff -Nru a/arch/i386/kernel/timers/timer_pit.c b/arch/i386/kernel/timers/t=
imer_pit.c
--- a/arch/i386/kernel/timers/timer_pit.c Tue Mar 25 15:48:49 2003
+++ b/arch/i386/kernel/timers/timer_pit.c Tue Mar 25 15:48:49 2003
@@ -27,6 +27,11 @@
/* nothing needed */
}
=20
+static unsigned long long monotonic_clock_pit(void)
+{
+ return 0;
+}
+
static void delay_pit(unsigned long loops)
{
int d0;
@@ -141,5 +146,6 @@
.init =3D init_pit,=20
.mark_offset =3D mark_offset_pit,=20
.get_offset =3D get_offset_pit,
+ .monotonic_clock =3D monotonic_clock_pit,
.delay =3D delay_pit,
};
diff -Nru a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/t=
imer_tsc.c
--- a/arch/i386/kernel/timers/timer_tsc.c Tue Mar 25 15:48:49 2003
+++ b/arch/i386/kernel/timers/timer_tsc.c Tue Mar 25 15:48:49 2003
@@ -23,6 +23,38 @@
static int delay_at_last_interrupt;
=20
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;
+
+
+/* convert from cycles(64bits) =3D> nanoseconds (64bits)
+ * basic equation:
+ * ns =3D cycles / (freq / ns_per_sec)
+ * ns =3D cycles * (ns_per_sec / freq)
+ * ns =3D cycles * (10^9 / (cpu_mhz * 10^6))
+ * ns =3D cycles * (10^3 / cpu_mhz)
+ *
+ * Then we use scaling math (suggested by george@mvista.com) to get:
+ * ns =3D cycles * (10^3 * SC / cpu_mhz) / SC
+ * ns =3D cycles * cyc2ns_scale / SC
+ *
+ * And since SC is a constant power of two, we can convert the div
+ * into a shift. =20
+ * -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ */
+static unsigned long cyc2ns_scale;=20
+#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen*/
+
+static inline void set_cyc2ns_scale(unsigned long cpu_mhz)
+{
+ cyc2ns_scale =3D (1000 << CYC2NS_SCALE_FACTOR)/cpu_mhz;
+}
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+ return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
+}
+
=20
/* Cached *multiplier* to convert TSC counts to microseconds.
* (see the equation below).
@@ -60,11 +92,25 @@
return delay_at_last_interrupt + edx;
}
=20
+static unsigned long long monotonic_clock_tsc(void)
+{
+ unsigned long long last_offset, this_offset;
+ last_offset =3D ((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=3D0, count2=3DLATCH;
+ unsigned long long this_offset, last_offset;
+ last_offset =3D ((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 +125,7 @@
=09
/* read Pentium cycle counter */
=20
- rdtscl(last_tsc_low);
+ rdtsc(last_tsc_low, last_tsc_high);
=20
spin_lock(&i8253_lock);
outb_p(0x00, 0x43); /* latch the count ASAP */
@@ -104,6 +150,11 @@
=20
count =3D ((LATCH-1) - count) * TICK_SIZE;
delay_at_last_interrupt =3D (count + LATCH/2) / LATCH;
+=09
+ /* update the monotonic base value */
+ this_offset =3D ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
+ monotonic_base +=3D cycles_2_ns(this_offset - last_offset);
+
}
=20
static void delay_tsc(unsigned long loops)
@@ -295,6 +346,7 @@
"0" (eax), "1" (edx));
printk("Detected %lu.%03lu MHz processor.\n", cpu_khz / 1000, cpu_khz =
% 1000);
}
+ set_cyc2ns_scale(cpu_khz/1000);
return 0;
}
}
@@ -328,5 +380,6 @@
.init =3D init_tsc,
.mark_offset =3D mark_offset_tsc,=20
.get_offset =3D get_offset_tsc,
+ .monotonic_clock =3D monotonic_clock_tsc,
.delay =3D delay_tsc,
};
diff -Nru a/drivers/char/hangcheck-timer.c b/drivers/char/hangcheck-timer.c
--- a/drivers/char/hangcheck-timer.c Tue Mar 25 15:48:49 2003
+++ b/drivers/char/hangcheck-timer.c Tue Mar 25 15:48:49 2003
@@ -78,11 +78,13 @@
static struct timer_list hangcheck_ticktock =3D
TIMER_INITIALIZER(hangcheck_fire, 0, 0);
=20
+extern unsigned long long monotonic_clock(void);
+
static void hangcheck_fire(unsigned long data)
{
unsigned long long cur_tsc, tsc_diff;
=20
- cur_tsc =3D get_cycles();
+ cur_tsc =3D monotonic_clock();
=20
if (cur_tsc > hangcheck_tsc)
tsc_diff =3D cur_tsc - hangcheck_tsc;
@@ -98,7 +100,7 @@
}
}
mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
- hangcheck_tsc =3D get_cycles();
+ hangcheck_tsc =3D monotonic_clock();
}
=20
=20
@@ -108,10 +110,10 @@
VERSION_STR, hangcheck_tick, hangcheck_margin);
=20
hangcheck_tsc_margin =3D hangcheck_margin + hangcheck_tick;
- hangcheck_tsc_margin *=3D HZ;
- hangcheck_tsc_margin *=3D current_cpu_data.loops_per_jiffy;
+ hangcheck_tsc_margin *=3D 1000000000;
+
=20
- hangcheck_tsc =3D get_cycles();
+ hangcheck_tsc =3D monotonic_clock();
mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
=20
return 0;
diff -Nru a/include/asm-i386/timer.h b/include/asm-i386/timer.h
--- a/include/asm-i386/timer.h Tue Mar 25 15:48:49 2003
+++ b/include/asm-i386/timer.h Tue Mar 25 15:48:49 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);
};
=20
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