Re: [PATCH] - Optional method to purge the TLB on SN systems

[Zou Nan hai <nanhai.zou@intel.com>]

On Wed, 2007-03-28 at 03:39, Jack Steiner wrote:

> This patch adds an optional method for purging the TLB on SN IA64 systems.
> The change should not affect any non-SN system.
> 
> 	Signed-off-by: Jack Steiner <steiner@sgi.com>
> 
> ---
> 
> +void
> +smp_flush_tlb_cpumask (cpumask_t xcpumask)
> +{
> +	unsigned short counts[NR_CPUS];
> +	cpumask_t cpumask = xcpumask;
> +	int count, mycpu, cpu, flush_mycpu = 0;
> +
> +	preempt_disable();
> +	mycpu = smp_processor_id();
> +
> +	for_each_cpu_mask(cpu, cpumask) {
> +		counts[cpu] = per_cpu(local_flush_count, cpu);
> +		mb();
> +		if (cpu = mycpu)
> +			flush_mycpu = 1;
> +		else
> +			smp_send_local_flush_tlb(cpu);
> +	}
> +
> +	if (flush_mycpu)
> +		smp_local_flush_tlb();
> +
> +	for_each_cpu_mask(cpu, cpumask) {
> +		count = 0;
> +		while(counts[cpu] = per_cpu(local_flush_count, cpu)) {

Due to 64k offset of percpu data, the same percpu variable on different
CPUs are very likely to be on the same cacheline of some levels of
cache.

So I think the operation on local_flush_count may be very cache
unfriendly...


Zou Nan hai