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[IA64] disable preemption in udelay()

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The udelay() inline for ia64 uses the ITC.  If CONFIG_PREEMPT is enabled
and the platform has unsynchronized ITCs and the calling task migrates
to another CPU while doing the udelay loop, then the effective delay may
be too short or very, very long.

This patch disables preemption around 100 usec chunks of the overall
desired udelay time.  This minimizes preemption-holdoffs.

udelay() is now too big to be inline, move it out of line and export it.

Signed-off-by: John Hawkes <hawkes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
John Hawkes 2005-12-16 10:00:24 -08:00 committed by Tony Luck
parent 7b6666530e
commit f5899b5d4f
2 changed files with 30 additions and 9 deletions
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29
arch/ia64/kernel/time.c
View File

@ -249,3 +249,32 @@ time_init (void)
*/
set_normalized_timespec(&wall_to_monotonic, -xtime.tv_sec, -xtime.tv_nsec);
}
#define SMALLUSECS 100
void
udelay (unsigned long usecs)
{
unsigned long start;
unsigned long cycles;
unsigned long smallusecs;
/*
* Execute the non-preemptible delay loop (because the ITC might
* not be synchronized between CPUS) in relatively short time
* chunks, allowing preemption between the chunks.
*/
while (usecs > 0) {
smallusecs = (usecs > SMALLUSECS) ? SMALLUSECS : usecs;
preempt_disable();
cycles = smallusecs*local_cpu_data->cyc_per_usec;
start = ia64_get_itc();
while (ia64_get_itc() - start < cycles)
cpu_relax();
preempt_enable();
usecs -= smallusecs;
}
}
EXPORT_SYMBOL(udelay);

10
include/asm-ia64/delay.h
View File

@ -84,14 +84,6 @@ __delay (unsigned long loops)
ia64_delay_loop (loops - 1);
}
static __inline__ void
udelay (unsigned long usecs)
{
unsigned long start = ia64_get_itc();
unsigned long cycles = usecs*local_cpu_data->cyc_per_usec;
while (ia64_get_itc() - start < cycles)
cpu_relax();
}
extern void udelay (unsigned long usecs);
#endif /* _ASM_IA64_DELAY_H */