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Subject[PATCH 23/23] clocksource tsc: add verify routine
I've included this as another user of the clocksource interface. I don't see a
usage for this across all achitectures. So a fully generic version isn't needed.

I modified this from the pre 2.6.20-rc6-mm2 release to make the routine smaller
and to make it select a clocksource inside the timer. It should work with an HPET.

Signed-Off-By: Daniel Walker <dwalker@mvista.com>

---
arch/i386/kernel/tsc.c | 55 ++++++++++++++++++++++++++++----------------
include/linux/clocksource.h | 16 ++++++++++++
2 files changed, 51 insertions(+), 20 deletions(-)
Index: linux-2.6.19/arch/i386/kernel/tsc.c
===================================================================
--- linux-2.6.19.orig/arch/i386/kernel/tsc.c
+++ linux-2.6.19/arch/i386/kernel/tsc.c
@@ -343,47 +343,59 @@ static struct dmi_system_id __initdata b
{}
};

-#define TSC_FREQ_CHECK_INTERVAL (10*MSEC_PER_SEC) /* 10sec in MS */
+#define WATCHDOG_TRESHOLD (NSEC_PER_SEC >> 4)
+#define TSC_FREQ_CHECK_INTERVAL (MSEC_PER_SEC/2)
static struct timer_list verify_tsc_freq_timer;
+struct clocksource *verify_clock;

/* XXX - Probably should add locking */
static void verify_tsc_freq(unsigned long unused)
{
- static u64 last_tsc;
- static unsigned long last_jiffies;
-
- u64 now_tsc, interval_tsc;
- unsigned long now_jiffies, interval_jiffies;
+ static cycle_t last_tsc, last_verify;

+ cycle_t now_tsc, verify_clock_now, interval;
+ s64 nsecs;

if (check_tsc_unstable())
return;

- rdtscll(now_tsc);
- now_jiffies = jiffies;
+ if (unlikely(system_state != SYSTEM_RUNNING))
+ goto out_timer;

- if (!last_jiffies) {
- goto out;
+ if (unlikely(!verify_clock)) {
+ verify_clock =
+ clocksource_get_masked_clock(CLOCKSOURCE_PM_AFFECTED);
+ printk("TSC: selected %s clocksource for TSC verification.\n",
+ verify_clock->name);
}

- interval_jiffies = now_jiffies - last_jiffies;
- interval_tsc = now_tsc - last_tsc;
- interval_tsc *= HZ;
- do_div(interval_tsc, cpu_khz*1000);
+ now_tsc = clocksource_read(&clocksource_tsc);
+ verify_clock_now = clocksource_read(verify_clock);
+
+ if (!last_tsc)
+ goto out;

- if (interval_tsc < (interval_jiffies * 3 / 4)) {
+ interval = clocksource_subtract(verify_clock, verify_clock_now,
+ last_verify);
+ nsecs = cyc2ns(verify_clock, interval);
+
+ interval = clocksource_subtract(&clocksource_tsc, now_tsc, last_tsc);
+ nsecs -= cyc2ns(&clocksource_tsc, interval);
+
+ if (nsecs > WATCHDOG_TRESHOLD) {
printk("TSC appears to be running slowly. "
- "Marking it as unstable\n");
+ "Marking it as unstable");
mark_tsc_unstable();
return;
}

out:
- last_tsc = now_tsc;
- last_jiffies = now_jiffies;
+ last_tsc = now_tsc;
+ last_verify = verify_clock_now;
+out_timer:
/* set us up to go off on the next interval: */
mod_timer(&verify_tsc_freq_timer,
- jiffies + msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL));
+ jiffies + msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL));
}

/*
@@ -444,7 +456,10 @@ static int __init init_tsc_clocksource(v
if (check_tsc_unstable())
clocksource_tsc.flags |= CLOCKSOURCE_UNSTABLE |
CLOCKSOURCE_NOT_CONTINUOUS;
-
+ /*
+ * The verify routine will select the right clock after the
+ * system boots fully.
+ */
init_timer(&verify_tsc_freq_timer);
verify_tsc_freq_timer.function = verify_tsc_freq;
verify_tsc_freq_timer.expires =
Index: linux-2.6.19/include/linux/clocksource.h
===================================================================
--- linux-2.6.19.orig/include/linux/clocksource.h
+++ linux-2.6.19/include/linux/clocksource.h
@@ -207,6 +207,22 @@ static inline s64 cyc2ns(struct clocksou
}

/**
+ * clocksource_subtract - Subtract two cycle_t timestamps
+ * @cs: Clocksource the timestamp came from
+ * @stop: Stop timestamp
+ * @start: Start timestamp
+ *
+ * This subtract accounts for rollover by using the clocksource mask.
+ * The clock can roll over only once, after that this subtract will not
+ * work properly.
+ */
+static inline s64 clocksource_subtract(struct clocksource* cs, cycle_t stop,
+ cycle_t start)
+{
+ return ((stop - start) & cs->mask);
+}
+
+/**
* clocksource_calculate_interval - Calculates a clocksource interval struct
*
* @c: Pointer to clocksource.
--
-
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