On Sun, Mar 23, 2025 at 10:20:37AM +0000, Damien Zammit wrote:
> You probably want to disable it entirely so it doesn't need to execute a
> branch condition every time it reads the timer, ie with #ifdef.
> This code path would be critical for timing.
Fair enough :/. Thanks :).
Zhaoming
>
>
> -------- Original Message --------
> On 23/3/25 9:13 pm, Zhaoming Luo <zhming...@163.com> wrote:
>
> > Hi,
> >
> > I'm wondering the code for checking whether a high-precision code is
> > available should be in mach_clock.c or in the machine-dependent
> > directory. In this patch it's in the machine-dependent directory. It can
> > ensure the backward compactability. Otherwise compiling a gnumach with
> > only '../configure' will cause page fault at the startup.
> > ```
> > +uint32_t
> > +hpclock_read_counter(void)
> > +{
> > + if (hpet_addr != NULL)
> > + return HPET32(HPET_COUNTER);
> > + else
> > + return 0;
> > +}
> > +
> > +uint32_t
> > +hpclock_get_counter_period_nsec(void)
> > +{
> > + if (hpet_addr != NULL)
> > + return hpet_period_nsec;
> > + else
> > + return 0;
> > +}
> > ```
> >
> > Zhaoming
> > ---
> > i386/i386/apic.c | 17 +++++++++++++++++
> > i386/i386at/model_dep.c | 2 ++
> > kern/mach_clock.c | 36 +++++++++++++++++++++++++++++++++++-
> > kern/mach_clock.h | 4 ++++
> > 4 files changed, 58 insertions(+), 1 deletion(-)
> >
> > diff --git a/i386/i386/apic.c b/i386/i386/apic.c
> > index 77d555b5..6cacd5fa 100644
> > --- a/i386/i386/apic.c
> > +++ b/i386/i386/apic.c
> > @@ -479,3 +479,20 @@ hpet_mdelay(uint32_t ms)
> > hpet_udelay(ms * 1000);
> > }
> >
> > +uint32_t
> > +hpclock_read_counter(void)
> > +{
> > + if (hpet_addr != NULL)
> > + return HPET32(HPET_COUNTER);
> > + else
> > + return 0;
> > +}
> > +
> > +uint32_t
> > +hpclock_get_counter_period_nsec(void)
> > +{
> > + if (hpet_addr != NULL)
> > + return hpet_period_nsec;
> > + else
> > + return 0;
> > +}
> > diff --git a/i386/i386at/model_dep.c b/i386/i386at/model_dep.c
> > index 30449c37..42dadeb8 100644
> > --- a/i386/i386at/model_dep.c
> > +++ b/i386/i386at/model_dep.c
> > @@ -223,7 +223,9 @@ void machine_init(void)
> > */
> > gdt_descr_tmp.linear_base += apboot_addr;
> > apboot_jmp_offset += apboot_addr;
> > +#endif
> >
> > +#ifdef APIC
> > /*
> > * Initialize the HPET
> > */
> > diff --git a/kern/mach_clock.c b/kern/mach_clock.c
> > index 5501b7b8..9bae3439 100644
> > --- a/kern/mach_clock.c
> > +++ b/kern/mach_clock.c
> > @@ -83,6 +83,15 @@ unsigned tickadj = 500 / HZ; /* can adjust
> > 100 usecs per second */
> > unsigned bigadj = 1000000; /* adjust 10*tickadj if adjustment
> > > bigadj */
> >
> > +/* A high-precision (hardware) clock is taken into account to increase the
> > + * accuracy of the functions used for getting time (e.g.
> > host_get_time64()).
> > + * The counter of the clock is read once in every clock interrupt. When
> > any
> > + * of the functions used for getting time is called, the counter is read
> > again
> > + * and the difference between these two read is multiplied by the counter
> > + * period and added to the read value from time or uptime to get a more
> > + * accurate time read. */
> > +uint32_t last_hpc_read = 0;
> > +
> > /*
> > * This update protocol, with a check value, allows
> > * do {
> > @@ -128,7 +137,8 @@ MACRO_BEGIN
> > \
> > __sync_synchronize(); \
> > (time)->nanoseconds = mtime->time_value.nanoseconds; \
> > __sync_synchronize(); \
> > - } while ((time)->seconds != mtime->check_seconds64); \
> > + } while ((time)->seconds != mtime->check_seconds64); \
> > + time_value64_add_hpc(time); \
> > MACRO_END
> >
> > #define read_mapped_uptime(uptime)
> > \
> > @@ -139,6 +149,7 @@ MACRO_BEGIN
> > \
> > (uptime)->nanoseconds = mtime->uptime_value.nanoseconds;\
> > __sync_synchronize(); \
> > } while ((uptime)->seconds != mtime->check_upseconds64); \
> > + time_value64_add_hpc(uptime); \
> > MACRO_END
> >
> > def_simple_lock_irq_data(static, timer_lock) /* lock for ... */
> > @@ -292,6 +303,7 @@ void clock_interrupt(
> > }
> > }
> > }
> > + last_hpc_read = hpclock_read_counter();
> > }
> >
> > /*
> > @@ -426,6 +438,28 @@ clock_boottime_update(const struct time_value64
> > *new_time)
> > time_value64_add(&clock_boottime_offset, &delta);
> > }
> >
> > +/*
> > + * Add the time value since last clock interrupt in nanosecond.
> > + */
> > +static void
> > +time_value64_add_hpc(time_value64_t *value)
> > +{
> > + uint32_t now = hpclock_read_counter();
> > + /* Time since last clock interrupt in nanosecond. */
> > + int64_t ns = (now - last_hpc_read) * hpclock_get_counter_period_nsec();
> > +
> > + /* Limit the value of ns under the period of a clock interrupt in case
> > + imprecise computation causes ns greater than the clock interrupt
> > + period. */
> > + if (ns > tick * 1000)
> > + /* Let ns stuck at the end of the clock interrupt period when
> > + something bad happens. */
> > + ns = (tick * 1000) - 1;
> > +
> > + time_value64_add_nanos(value, ns);
> > +}
> > +
> > +
> > /*
> > * Record a timestamp in STAMP. Records values in the boot-time clock
> > * frame.
> > diff --git a/kern/mach_clock.h b/kern/mach_clock.h
> > index d4f04f5e..e83b638c 100644
> > --- a/kern/mach_clock.h
> > +++ b/kern/mach_clock.h
> > @@ -110,4 +110,8 @@ extern boolean_t untimeout(timer_func_t *fcn, const
> > void *param);
> > extern int timeopen(dev_t dev, int flag, io_req_t ior);
> > extern void timeclose(dev_t dev, int flag);
> >
> > +/* For high-precision clocks. */
> > +extern uint32_t hpclock_read_counter(void);
> > +extern uint32_t hpclock_get_counter_period_nsec(void);
> > +
> > #endif /* _KERN_MACH_CLOCK_H_ */
> > --
> > 2.47.2
> >
> >
> >
