From: Johannes Weiner <[email protected]>
Switch to GENERIC_TIME by using the ccount register as a clock source.
Signed-off-by: Johannes Weiner <[email protected]>
---
arch/xtensa/Kconfig | 3 +
arch/xtensa/kernel/time.c | 92 ++++++++++------------------------------------
2 files changed, 23 insertions(+), 72 deletions(-)
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -45,6 +45,9 @@ config HZ
int
default 100
+config GENERIC_TIME
+ def_bool y
+
source "init/Kconfig"
source "kernel/Kconfig.freezer"
--- a/arch/xtensa/kernel/time.c
+++ b/arch/xtensa/kernel/time.c
@@ -14,6 +14,7 @@
#include <linux/errno.h>
#include <linux/time.h>
+#include <linux/clocksource.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/init.h>
@@ -29,6 +30,19 @@ unsigned long ccount_per_jiffy; /* per
unsigned long nsec_per_ccount; /* nsec per ccount increment */
#endif
+static cycle_t ccount_read(void)
+{
+ return (cycle_t)get_ccount();
+}
+
+static struct clocksource ccount_clocksource = {
+ .name = "ccount",
+ .rating = 200,
+ .read = ccount_read,
+ .mask = CLOCKSOURCE_MASK(32),
+ .mult = NSEC_PER_CCOUNT,
+};
+
static irqreturn_t timer_interrupt(int irq, void *dev_id);
static struct irqaction timer_irqaction = {
.handler = timer_interrupt,
@@ -38,9 +52,11 @@ static struct irqaction timer_irqaction
void __init time_init(void)
{
- /* The platform must provide a function to calibrate the processor
- * speed for the CALIBRATE.
- */
+ xtime.tv_nsec = 0;
+ xtime.tv_sec = read_persistent_clock();
+
+ set_normalized_timespec(&wall_to_monotonic,
+ -xtime.tv_sec, -xtime.tv_nsec);
#ifdef CONFIG_XTENSA_CALIBRATE_CCOUNT
printk("Calibrating CPU frequency ");
@@ -48,12 +64,7 @@ void __init time_init(void)
printk("%d.%02d MHz\n", (int)ccount_per_jiffy/(1000000/HZ),
(int)(ccount_per_jiffy/(10000/HZ))%100);
#endif
-
- xtime.tv_nsec = 0;
- xtime.tv_sec = read_persistent_clock();
-
- set_normalized_timespec(&wall_to_monotonic,
- -xtime.tv_sec, -xtime.tv_nsec);
+ clocksource_register(&ccount_clocksource);
/* Initialize the linux timer interrupt. */
@@ -61,69 +72,6 @@ void __init time_init(void)
set_linux_timer(get_ccount() + CCOUNT_PER_JIFFY);
}
-
-int do_settimeofday(struct timespec *tv)
-{
- time_t wtm_sec, sec = tv->tv_sec;
- long wtm_nsec, nsec = tv->tv_nsec;
- unsigned long delta;
-
- if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
- return -EINVAL;
-
- write_seqlock_irq(&xtime_lock);
-
- /* This is revolting. We need to set "xtime" correctly. However, the
- * value in this location is the value at the most recent update of
- * wall time. Discover what correction gettimeofday() would have
- * made, and then undo it!
- */
-
- delta = CCOUNT_PER_JIFFY;
- delta += get_ccount() - get_linux_timer();
- nsec -= delta * NSEC_PER_CCOUNT;
-
- wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
- wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
-
- set_normalized_timespec(&xtime, sec, nsec);
- set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
-
- ntp_clear();
- write_sequnlock_irq(&xtime_lock);
- return 0;
-}
-
-EXPORT_SYMBOL(do_settimeofday);
-
-
-void do_gettimeofday(struct timeval *tv)
-{
- unsigned long flags;
- unsigned long volatile sec, usec, delta, seq;
-
- do {
- seq = read_seqbegin_irqsave(&xtime_lock, flags);
-
- sec = xtime.tv_sec;
- usec = (xtime.tv_nsec / NSEC_PER_USEC);
-
- delta = get_linux_timer() - get_ccount();
-
- } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
-
- usec += (((unsigned long) CCOUNT_PER_JIFFY - delta)
- * (unsigned long) NSEC_PER_CCOUNT) / NSEC_PER_USEC;
-
- for (; usec >= 1000000; sec++, usec -= 1000000)
- ;
-
- tv->tv_sec = sec;
- tv->tv_usec = usec;
-}
-
-EXPORT_SYMBOL(do_gettimeofday);
-
/*
* The timer interrupt is called HZ times per second.
*/
--
On Tue, 2009-03-03 at 16:30 +0100, Johannes Weiner wrote:
> @ -29,6 +30,19 @@ unsigned long ccount_per_jiffy; /* per
> unsigned long nsec_per_ccount; /* nsec per ccount increment
> */
> #endif
>
> +static cycle_t ccount_read(void)
> +{
> + return (cycle_t)get_ccount();
> +}
> +
> +static struct clocksource ccount_clocksource = {
> + .name = "ccount",
> + .rating = 200,
> + .read = ccount_read,
> + .mask = CLOCKSOURCE_MASK(32),
> + .mult = NSEC_PER_CCOUNT,
> +};
You don't want to use the shift field?
Daniel
On Tue, Mar 03, 2009 at 09:55:45AM -0800, Daniel Walker wrote:
> On Tue, 2009-03-03 at 16:30 +0100, Johannes Weiner wrote:
> > @ -29,6 +30,19 @@ unsigned long ccount_per_jiffy; /* per
> > unsigned long nsec_per_ccount; /* nsec per ccount increment
> > */
> > #endif
> >
> > +static cycle_t ccount_read(void)
> > +{
> > + return (cycle_t)get_ccount();
> > +}
> > +
> > +static struct clocksource ccount_clocksource = {
> > + .name = "ccount",
> > + .rating = 200,
> > + .read = ccount_read,
> > + .mask = CLOCKSOURCE_MASK(32),
> > + .mult = NSEC_PER_CCOUNT,
> > +};
>
> You don't want to use the shift field?
Thanks for pointing it out.
To make sure I understood this:
If shift is 0, then a walltime adjustment would be done in 1/2^0
steps, meaning an adjustment of counting one nanosecond more or less
per ccount.
To give this a finer granularity and smooth out adjustments, the shift
should be a trade-off between too much adjustment and no adjustment
progress in a sane amount of time (and, of course, to stay within
bounds of the used type).
Does that make sense?
I found a patch of yours that introduced clocksource_hz2shift() but it
seems it hasn't been merged (yet). Is it yet to get integrated?
Thanks in advance,
Hannes
On Tue, 2009-03-03 at 20:54 +0100, Johannes Weiner wrote:
> On Tue, Mar 03, 2009 at 09:55:45AM -0800, Daniel Walker wrote:
> > On Tue, 2009-03-03 at 16:30 +0100, Johannes Weiner wrote:
> > > @ -29,6 +30,19 @@ unsigned long ccount_per_jiffy; /* per
> > > unsigned long nsec_per_ccount; /* nsec per ccount increment
> > > */
> > > #endif
> > >
> > > +static cycle_t ccount_read(void)
> > > +{
> > > + return (cycle_t)get_ccount();
> > > +}
> > > +
> > > +static struct clocksource ccount_clocksource = {
> > > + .name = "ccount",
> > > + .rating = 200,
> > > + .read = ccount_read,
> > > + .mask = CLOCKSOURCE_MASK(32),
> > > + .mult = NSEC_PER_CCOUNT,
> > > +};
> >
> > You don't want to use the shift field?
>
> Thanks for pointing it out.
>
> To make sure I understood this:
>
> If shift is 0, then a walltime adjustment would be done in 1/2^0
> steps, meaning an adjustment of counting one nanosecond more or less
> per ccount.
The shift and mult are just used to convert your cycle counters current
count into nanoseconds .. I'm not sure how much a zero shift would
degrade the conversion to nanoseconds for your cycles counter tho. So it
could be along the lines of what your suggesting above.
> To give this a finer granularity and smooth out adjustments, the shift
> should be a trade-off between too much adjustment and no adjustment
> progress in a sane amount of time (and, of course, to stay within
> bounds of the used type).
>
> Does that make sense?
I don't really look at it in terms of walltime adjustments. The actual
frequency of kernel time adjustments isn't defined in the clocksource
structure AFAIK. From my experience you just want the clocksource to
produce the most accurate nanosecond value your hardware can provide ,
which would mean setting the shift as high as is safe for your hardware.
I added John Stultz to the CC so he could comment further if he cares
too.
> I found a patch of yours that introduced clocksource_hz2shift() but it
> seems it hasn't been merged (yet). Is it yet to get integrated?
I've been meaning to update it, but haven't gotten around to it. If you
know the input values you can run that function once just to produce a
shift which you define statically in the clocksource structure. Then use
that shift value with the other helper clocksource_hz2mult() to produce
a mult value.
Daniel
On Tue, Mar 03, 2009 at 01:36:04PM -0800, Daniel Walker wrote:
> On Tue, 2009-03-03 at 20:54 +0100, Johannes Weiner wrote:
> > On Tue, Mar 03, 2009 at 09:55:45AM -0800, Daniel Walker wrote:
> > > On Tue, 2009-03-03 at 16:30 +0100, Johannes Weiner wrote:
> > > > @ -29,6 +30,19 @@ unsigned long ccount_per_jiffy; /* per
> > > > unsigned long nsec_per_ccount; /* nsec per ccount increment
> > > > */
> > > > #endif
> > > >
> > > > +static cycle_t ccount_read(void)
> > > > +{
> > > > + return (cycle_t)get_ccount();
> > > > +}
> > > > +
> > > > +static struct clocksource ccount_clocksource = {
> > > > + .name = "ccount",
> > > > + .rating = 200,
> > > > + .read = ccount_read,
> > > > + .mask = CLOCKSOURCE_MASK(32),
> > > > + .mult = NSEC_PER_CCOUNT,
> > > > +};
> > >
> > > You don't want to use the shift field?
> >
> > Thanks for pointing it out.
> >
> > To make sure I understood this:
> >
> > If shift is 0, then a walltime adjustment would be done in 1/2^0
> > steps, meaning an adjustment of counting one nanosecond more or less
> > per ccount.
>
> The shift and mult are just used to convert your cycle counters current
> count into nanoseconds .. I'm not sure how much a zero shift would
> degrade the conversion to nanoseconds for your cycles counter tho. So it
> could be along the lines of what your suggesting above.
>
> > To give this a finer granularity and smooth out adjustments, the shift
> > should be a trade-off between too much adjustment and no adjustment
> > progress in a sane amount of time (and, of course, to stay within
> > bounds of the used type).
> >
> > Does that make sense?
>
> I don't really look at it in terms of walltime adjustments. The actual
> frequency of kernel time adjustments isn't defined in the clocksource
> structure AFAIK. From my experience you just want the clocksource to
> produce the most accurate nanosecond value your hardware can provide ,
> which would mean setting the shift as high as is safe for your hardware.
>
> I added John Stultz to the CC so he could comment further if he cares
> too.
>
> > I found a patch of yours that introduced clocksource_hz2shift() but it
> > seems it hasn't been merged (yet). Is it yet to get integrated?
>
> I've been meaning to update it, but haven't gotten around to it. If you
> know the input values you can run that function once just to produce a
> shift which you define statically in the clocksource structure. Then use
> that shift value with the other helper clocksource_hz2mult() to produce
> a mult value.
Ok, here is version 2. The shift now limits the CPU clock to a
minimum of 1 MHz, comment in the code. I think the trade-off should
be okay. John? Chris?
---
Subject: xtensa: ccount clocksource
From: Johannes Weiner <[email protected]>
Switch to GENERIC_TIME by using the ccount register as a clock source.
Signed-off-by: Johannes Weiner <[email protected]>
---
arch/xtensa/Kconfig | 3 +
arch/xtensa/kernel/time.c | 103 +++++++++++++---------------------------------
2 files changed, 33 insertions(+), 73 deletions(-)
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -48,6 +48,9 @@ config HZ
int
default 100
+config GENERIC_TIME
+ def_bool y
+
source "init/Kconfig"
source "kernel/Kconfig.freezer"
--- a/arch/xtensa/kernel/time.c
+++ b/arch/xtensa/kernel/time.c
@@ -14,6 +14,7 @@
#include <linux/errno.h>
#include <linux/time.h>
+#include <linux/clocksource.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/init.h>
@@ -29,6 +30,26 @@ unsigned long ccount_per_jiffy; /* per
unsigned long nsec_per_ccount; /* nsec per ccount increment */
#endif
+static cycle_t ccount_read(void)
+{
+ return (cycle_t)get_ccount();
+}
+
+static struct clocksource ccount_clocksource = {
+ .name = "ccount",
+ .rating = 200,
+ .read = ccount_read,
+ .mask = CLOCKSOURCE_MASK(32),
+ /*
+ * With a shift of 22 the lower limit of the cpu clock is
+ * 1MHz, where NSEC_PER_CCOUNT is 1000 or a bit less than
+ * 2^10: Since we have 32 bits and the multiplicator can
+ * already take up as much as 10 bits, this leaves us with
+ * remaining upper 22 bits.
+ */
+ .shift = 22,
+};
+
static irqreturn_t timer_interrupt(int irq, void *dev_id);
static struct irqaction timer_irqaction = {
.handler = timer_interrupt,
@@ -38,9 +59,11 @@ static struct irqaction timer_irqaction
void __init time_init(void)
{
- /* The platform must provide a function to calibrate the processor
- * speed for the CALIBRATE.
- */
+ xtime.tv_nsec = 0;
+ xtime.tv_sec = read_persistent_clock();
+
+ set_normalized_timespec(&wall_to_monotonic,
+ -xtime.tv_sec, -xtime.tv_nsec);
#ifdef CONFIG_XTENSA_CALIBRATE_CCOUNT
printk("Calibrating CPU frequency ");
@@ -48,12 +71,10 @@ void __init time_init(void)
printk("%d.%02d MHz\n", (int)ccount_per_jiffy/(1000000/HZ),
(int)(ccount_per_jiffy/(10000/HZ))%100);
#endif
-
- xtime.tv_nsec = 0;
- xtime.tv_sec = read_persistent_clock();
-
- set_normalized_timespec(&wall_to_monotonic,
- -xtime.tv_sec, -xtime.tv_nsec);
+ ccount_clocksource.mult =
+ clocksource_hz2mult(CCOUNT_PER_JIFFY * HZ,
+ ccount_clocksource.shift);
+ clocksource_register(&ccount_clocksource);
/* Initialize the linux timer interrupt. */
@@ -61,69 +82,6 @@ void __init time_init(void)
set_linux_timer(get_ccount() + CCOUNT_PER_JIFFY);
}
-
-int do_settimeofday(struct timespec *tv)
-{
- time_t wtm_sec, sec = tv->tv_sec;
- long wtm_nsec, nsec = tv->tv_nsec;
- unsigned long delta;
-
- if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
- return -EINVAL;
-
- write_seqlock_irq(&xtime_lock);
-
- /* This is revolting. We need to set "xtime" correctly. However, the
- * value in this location is the value at the most recent update of
- * wall time. Discover what correction gettimeofday() would have
- * made, and then undo it!
- */
-
- delta = CCOUNT_PER_JIFFY;
- delta += get_ccount() - get_linux_timer();
- nsec -= delta * NSEC_PER_CCOUNT;
-
- wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
- wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
-
- set_normalized_timespec(&xtime, sec, nsec);
- set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
-
- ntp_clear();
- write_sequnlock_irq(&xtime_lock);
- return 0;
-}
-
-EXPORT_SYMBOL(do_settimeofday);
-
-
-void do_gettimeofday(struct timeval *tv)
-{
- unsigned long flags;
- unsigned long volatile sec, usec, delta, seq;
-
- do {
- seq = read_seqbegin_irqsave(&xtime_lock, flags);
-
- sec = xtime.tv_sec;
- usec = (xtime.tv_nsec / NSEC_PER_USEC);
-
- delta = get_linux_timer() - get_ccount();
-
- } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
-
- usec += (((unsigned long) CCOUNT_PER_JIFFY - delta)
- * (unsigned long) NSEC_PER_CCOUNT) / NSEC_PER_USEC;
-
- for (; usec >= 1000000; sec++, usec -= 1000000)
- ;
-
- tv->tv_sec = sec;
- tv->tv_usec = usec;
-}
-
-EXPORT_SYMBOL(do_gettimeofday);
-
/*
* The timer interrupt is called HZ times per second.
*/
@@ -177,4 +135,3 @@ void __cpuinit calibrate_delay(void)
(loops_per_jiffy/(10000/HZ)) % 100);
}
#endif
-