Commit 4004c69a authored by Ravikiran G Thirumalai's avatar Ravikiran G Thirumalai Committed by Linus Torvalds
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Avoid too many remote cpu references due to /proc/stat 



Optimize show_stat to collect per-irq information just once.

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.
Considering the fact that we already compute this value per-cpu, we can
save on the remote references as below.

Signed-off-by: default avatarAlok N Kataria <alok.kataria@calsoftinc.com>
Signed-off-by: default avatarRavikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a0a99835

fs/proc/proc_misc.c

+12 −3
Original line number Diff line number Diff line
@@ -445,6 +445,11 @@ static int show_stat(struct seq_file *p, void *v) 
	cputime64_t user, nice, system, idle, iowait, irq, softirq, steal;

	u64 sum = 0;

	struct timespec boottime;

	unsigned int *per_irq_sum;



	per_irq_sum = kzalloc(sizeof(unsigned int)*NR_IRQS, GFP_KERNEL);

	if (!per_irq_sum)

		return -ENOMEM;



	user = nice = system = idle = iowait =

		irq = softirq = steal = cputime64_zero;
@@ -462,8 +467,11 @@ static int show_stat(struct seq_file *p, void *v) 
		irq = cputime64_add(irq, kstat_cpu(i).cpustat.irq);

		softirq = cputime64_add(softirq, kstat_cpu(i).cpustat.softirq);

		steal = cputime64_add(steal, kstat_cpu(i).cpustat.steal);

		for (j = 0 ; j < NR_IRQS ; j++)

			sum += kstat_cpu(i).irqs[j];

		for (j = 0; j < NR_IRQS; j++) {

			unsigned int temp = kstat_cpu(i).irqs[j];

			sum += temp;

			per_irq_sum[j] += temp;

		}

	}



	seq_printf(p, "cpu  %llu %llu %llu %llu %llu %llu %llu %llu\n",
@@ -501,7 +509,7 @@ static int show_stat(struct seq_file *p, void *v) 


#if !defined(CONFIG_PPC64) && !defined(CONFIG_ALPHA) && !defined(CONFIG_IA64)

	for (i = 0; i < NR_IRQS; i++)

		seq_printf(p, " %u", kstat_irqs(i));

		seq_printf(p, " %u", per_irq_sum[i]);

#endif



	seq_printf(p,
@@ -516,6 +524,7 @@ static int show_stat(struct seq_file *p, void *v) 
		nr_running(),

		nr_iowait());



	kfree(per_irq_sum);

	return 0;

}

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