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[POWERPC] Simplify smp_space_timers 

Greatly simplify the function smp_space_timers.

The stolen time calculation (per comment within the code) doesn't need the
half-jiffy stagger any more.  There isn't an issue with bouncing off global
locks, so we really shouldn't need any sort of staggering at all.

However, the last_jiffy value still needs to be set.   This removes the
extra stagger logic, and just sets the values.

This change should benefit applications that rely on barrier
synchronization, and will help cut down OS jitter.

Boot tested across the board (G5,power3,power4,power5,970mp blade).

Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
will schmidt 2007-05-11 23:34:16 +10:00 committed by Paul Mackerras
parent 435e0b2b16
commit e147ec8f18
1 changed files with 2 additions and 17 deletions
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19
arch/powerpc/kernel/time.c
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@ -711,30 +711,15 @@ void wakeup_decrementer(void)
void __init smp_space_timers(unsigned int max_cpus)
{
int i;
unsigned long half = tb_ticks_per_jiffy / 2;
unsigned long offset = tb_ticks_per_jiffy / max_cpus;
u64 previous_tb = per_cpu(last_jiffy, boot_cpuid);
/* make sure tb > per_cpu(last_jiffy, cpu) for all cpus always */
previous_tb -= tb_ticks_per_jiffy;
/*
* The stolen time calculation for POWER5 shared-processor LPAR
* systems works better if the two threads' timebase interrupts
* are staggered by half a jiffy with respect to each other.
*/
for_each_possible_cpu(i) {
if (i == boot_cpuid)
continue;
if (i == (boot_cpuid ^ 1))
per_cpu(last_jiffy, i) =
per_cpu(last_jiffy, boot_cpuid) - half;
else if (i & 1)
per_cpu(last_jiffy, i) =
per_cpu(last_jiffy, i ^ 1) + half;
else {
previous_tb += offset;
per_cpu(last_jiffy, i) = previous_tb;
}
per_cpu(last_jiffy, i) = previous_tb;
}
}
#endif