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Date: Tue, 12 Oct 2010 12:11:24 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Yinghai Lu <yinghai@...nel.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Jack Steiner <steiner@....com>, mingo@...e.hu, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] fix slowness of /proc/stat per-cpu IRQ sum calculation on large system by a new counter On Mon, 11 Oct 2010 20:05:59 -0700 Yinghai Lu <yinghai@...nel.org> wrote: kstat_cpu(i).cpustat.guest_nice); > > - for_each_irq_nr(j) { > > - sum += kstat_irqs_cpu(j, i); > > - } > > + sum = kstat_cpu_irqs_sum(i); > > should be > + sum += kstat_cpu_irqs_sum(i); > Ouch...thanks. == From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Problem: 'cat /proc/stat' is too slow on verrry bis system. /proc/stat shows the total number of all interrupts to each cpu. But when the number of IRQs are very large, it takes very long time and 'cat /proc/stat' takes more than 10 secs. This is because sum of all irq events are counted when /proc/stat is read. This patch adds "sum of all irq" counter percpu and update it at events. The cost of reading /proc/stat is important because it's used by major applications as 'top', 'ps', 'w', etc.... A test on a host (4096cpu, 256 nodes, 4592 irqs) shows %time cat /proc/stat > /dev/null Before Patch: 12.627 sec After Patch: 2.459 sec Changelog v1->v2: - fixed wrong update of a value "sum". Tested-by: Jack Steiner <steiner@....com> Acked-by: Jack Steiner <steiner@....com> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> --- fs/proc/stat.c | 4 +--- include/linux/kernel_stat.h | 14 ++++++++++++-- 2 files changed, 13 insertions(+), 5 deletions(-) Index: linux-2.6.36-rc7/fs/proc/stat.c =================================================================== --- linux-2.6.36-rc7.orig/fs/proc/stat.c +++ linux-2.6.36-rc7/fs/proc/stat.c @@ -52,9 +52,7 @@ static int show_stat(struct seq_file *p, guest = cputime64_add(guest, kstat_cpu(i).cpustat.guest); guest_nice = cputime64_add(guest_nice, kstat_cpu(i).cpustat.guest_nice); - for_each_irq_nr(j) { - sum += kstat_irqs_cpu(j, i); - } + sum += kstat_cpu_irqs_sum(i); sum += arch_irq_stat_cpu(i); for (j = 0; j < NR_SOFTIRQS; j++) { Index: linux-2.6.36-rc7/include/linux/kernel_stat.h =================================================================== --- linux-2.6.36-rc7.orig/include/linux/kernel_stat.h +++ linux-2.6.36-rc7/include/linux/kernel_stat.h @@ -33,6 +33,7 @@ struct kernel_stat { #ifndef CONFIG_GENERIC_HARDIRQS unsigned int irqs[NR_IRQS]; #endif + unsigned long irqs_sum; unsigned int softirqs[NR_SOFTIRQS]; }; @@ -54,6 +55,7 @@ static inline void kstat_incr_irqs_this_ struct irq_desc *desc) { kstat_this_cpu.irqs[irq]++; + kstat_this_cpu.irqs_sum++; } static inline unsigned int kstat_irqs_cpu(unsigned int irq, int cpu) @@ -65,8 +67,9 @@ static inline unsigned int kstat_irqs_cp extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu); #define kstat_irqs_this_cpu(DESC) \ ((DESC)->kstat_irqs[smp_processor_id()]) -#define kstat_incr_irqs_this_cpu(irqno, DESC) \ - ((DESC)->kstat_irqs[smp_processor_id()]++) +#define kstat_incr_irqs_this_cpu(irqno, DESC) do {\ + ((DESC)->kstat_irqs[smp_processor_id()]++);\ + kstat_this_cpu.irqs_sum++; } while (0) #endif @@ -94,6 +97,13 @@ static inline unsigned int kstat_irqs(un return sum; } +/* + * Number of interrupts per cpu, since bootup + */ +static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu) +{ + return kstat_cpu(cpu).irqs_sum; +} /* * Lock/unlock the current runqueue - to extract task statistics: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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