>>>>> On Mon, 19 May 2003 15:37:58 -0700 (PDT), "David S. Miller" <davem@redhat.com> said:
DaveM> That's not the issue, if I have only ONE way to do this on my
DaveM> platform, I can INLINE this thing and I DO NOT need function
DaveM> pointers.
With the present code, an architecture does not have to use any
indirect function calls if there is only one known interpolator
(presumably based on a CPU cycle counter). The only extra overhead is
the (inlined) read of variable time_interpolator and a check against
NULL. Is this acceptable?
For convenience, I attached the current proposal. In the SPARC case,
you'd simply never call register_time_interpolator() and use
arch-specific code to calculate (and update) last_nsec_offset. The
time_interpolator_update() and time_interpolator_reset() code then
take care of the rest.
--david
#ifdef CONFIG_TIME_INTERPOLATION
struct time_interpolator {
/* cache-hot stuff first: */
unsigned long (*get_offset) (void);
void (*update) (long);
void (*reset) (void);
/* cache-cold stuff follows here: */
struct time_interpolator *next;
unsigned long frequency; /* frequency in counts/second */
long drift; /* drift in parts-per-million (or -1) */
};
extern volatile unsigned long last_nsec_offset;
#ifndef __HAVE_ARCH_CMPXCHG
extern spin_lock_t last_nsec_offset_lock;
#endif
extern struct time_interpolator *time_interpolator;
extern void register_time_interpolator (struct time_interpolator *);
extern void unregister_time_interpolator (struct time_interpolator *);
/* Called with xtime read- OR write-lock acquired. */
static inline void
time_interpolator_update (long delta_nsec)
{
struct time_interpolator *ti = time_interpolator;
if (last_nsec_offset > 0) {
#ifdef __HAVE_ARCH_CMPXCHG
unsigned long new, old;
do {
old = last_nsec_offset;
if (old > delta_nsec)
new = old - delta_nsec;
else
new = 0;
} while (cmpxchg(&last_nsec_offset, old, new) != old);
#else
/*
* This really hurts, because it serializes gettimeofday(), but without an
* atomic single-word compare-and-exchange, there isn't all that much else
* we can do.
*/
spin_lock(&last_nsec_offset_lock);
{
last_nsec_offset -= min(last_nsec_offset, delta_nsec);
}
spin_unlock(&last_nsec_offset_lock);
#endif
}
if (ti)
(*ti->update)(delta_nsec);
}
/* Called with xtime read- or write-lock acquired. */
static inline void
time_interpolator_reset (void)
{
struct time_interpolator *ti = time_interpolator;
last_nsec_offset = 0;
if (ti)
(*ti->reset)();
}
static inline unsigned long
time_interpolator_get_offset (void)
{
struct time_interpolator *ti = time_interpolator;
if (ti)
return (*ti->get_offset)();
return last_nsec_offset;
}
#else /* !CONFIG_TIME_INTERPOLATION */
static inline void
time_interpolator_update (long delta_nsec)
{
}
static inline void
time_interpolator_reset (void)
{
}
static inline unsigned long
time_interpolator_get_offset (void)
{
return 0;
}
#endif /* !CONFIG_TIME_INTERPOLATION */
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This archive was generated by hypermail 2b29 : Fri May 23 2003 - 22:00:37 EST