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Subject[PATCH] [33/58] x86_64: Avoid too many remote cpu references due to /proc/stat
Date

From: Ravikiran G Thirumalai <kiran@scalex86.org>
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.
Can we disable computing/reporting this statistic? This piece of
statistic is not human readable on x86_64 anymore,

If not, can we optimize computing this statistic so as to avoid
too many remote references (patch to follow)

Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: Andi Kleen <ak@suse.de>

---
fs/proc/proc_misc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
Index: linux/fs/proc/proc_misc.c
===================================================================
--- linux.orig/fs/proc/proc_misc.c
+++ linux/fs/proc/proc_misc.c
@@ -499,7 +499,8 @@ static int show_stat(struct seq_file *p,
}
seq_printf(p, "intr %llu", (unsigned long long)sum);

-#if !defined(CONFIG_PPC64) && !defined(CONFIG_ALPHA) && !defined(CONFIG_IA64)
+#if !defined(CONFIG_PPC64) && !defined(CONFIG_ALPHA) && !defined(CONFIG_IA64) \
+ && !defined(CONFIG_X86_64)
for (i = 0; i < NR_IRQS; i++)
seq_printf(p, " %u", kstat_irqs(i));
#endif
-
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