Messages in this thread Patch in this message | | | Date | Thu, 21 Oct 2010 16:01:34 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | [PATCH v2 1/2] try to fix /proc/stat scalability of irq num per cpu |
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Posting an updated version against mmotm because I noticed rebase is necessary. (kernel/irq/handle.c is modified.) I'll post this again after merge window. == From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
/proc/stat shows the total number of all interrupts to each cpu. But when the number of IRQs are very large, it take 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 reduce read costs.
The cost of reading /proc/stat is important because it's used by major applications as 'top', 'ps', 'w', etc....
A test on a mechin (4096cpu, 256 nodes, 4592 irqs) shows
%time cat /proc/stat > /dev/null Before Patch: 12.627 sec After Patch: 2.459 sec
Tested-by: Jack Steiner <steiner@sgi.com> Acked-by: Jack Steiner <steiner@sgi.com> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> --- fs/proc/stat.c | 4 +--- include/linux/kernel_stat.h | 14 ++++++++++++-- 2 files changed, 13 insertions(+), 5 deletions(-)
Index: mmotm-1020/fs/proc/stat.c =================================================================== --- mmotm-1020.orig/fs/proc/stat.c +++ mmotm-1020/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: mmotm-1020/include/linux/kernel_stat.h =================================================================== --- mmotm-1020.orig/include/linux/kernel_stat.h +++ mmotm-1020/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:
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