x86_64: Avoid too many remote cpu references due to /proc/stat

Too many remote cpu references due to /proc/stat.

On x86_64, with newer kernel versions, kstat_irqs is a bit of a problem.
On every call to kstat_irqs, the process brings in per-cpu data from all
online cpus.  Doing this for NR_IRQS, which is now 256 + 32 * NR_CPUS
results in (256+32*63) * 63 remote cpu references on a 64 cpu config.
/proc/stat is parsed by common commands like top, who etc, causing lots
of cacheline transfers

This statistic seems useless.  Other 'big iron' arches disable this.

AK: changed to remove for all SMP setups
AK: add comment
Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/proc_misc.c

@@ -507,7 +507,8 @@ static int show_stat(struct seq_file *p, void *v)
 	}
 	seq_printf(p, "intr %llu", (unsigned long long)sum);
 
-#if !defined(CONFIG_PPC64) && !defined(CONFIG_ALPHA) && !defined(CONFIG_IA64)
+#ifndef CONFIG_SMP
+	/* Touches too many cache lines on SMP setups */
 	for (i = 0; i < NR_IRQS; i++)
 		seq_printf(p, " %u", per_irq_sum[i]);
 #endif