From db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d Mon Sep 17 00:00:00 2001 From: Jack Steiner Date: Fri, 31 Mar 2006 02:31:21 -0800 Subject: [PATCH] [PATCH] sched: reduce overhead of calc_load Currently, count_active_tasks() calls both nr_running() & nr_interruptible(). Each of these functions does a "for_each_cpu" & reads values from the runqueue of each cpu. Although this is not a lot of instructions, each runqueue may be located on different node. Depending on the architecture, a unique TLB entry may be required to access each runqueue. Since there may be more runqueues than cpu TLB entries, a scan of all runqueues can trash the TLB. Each memory reference incurs a TLB miss & refill. In addition, the runqueue cacheline that contains nr_running & nr_uninterruptible may be evicted from the cache between the two passes. This causes unnecessary cache misses. Combining nr_running() & nr_interruptible() into a single function substantially reduces the TLB & cache misses on large systems. This should have no measureable effect on smaller systems. On a 128p IA64 system running a memory stress workload, the new function reduced the overhead of calc_load() from 605 usec/call to 324 usec/call. Signed-off-by: Jack Steiner Acked-by: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/sched.h | 1 + kernel/sched.c | 15 +++++++++++++++ kernel/timer.c | 2 +- 3 files changed, 17 insertions(+), 1 deletion(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index d04186d8cc68..ab84adf5bb9a 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -100,6 +100,7 @@ DECLARE_PER_CPU(unsigned long, process_counts); extern int nr_processes(void); extern unsigned long nr_running(void); extern unsigned long nr_uninterruptible(void); +extern unsigned long nr_active(void); extern unsigned long nr_iowait(void); #include diff --git a/kernel/sched.c b/kernel/sched.c index a9ecac398bb9..6e52e0adff80 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1658,6 +1658,21 @@ unsigned long nr_iowait(void) return sum; } +unsigned long nr_active(void) +{ + unsigned long i, running = 0, uninterruptible = 0; + + for_each_online_cpu(i) { + running += cpu_rq(i)->nr_running; + uninterruptible += cpu_rq(i)->nr_uninterruptible; + } + + if (unlikely((long)uninterruptible < 0)) + uninterruptible = 0; + + return running + uninterruptible; +} + #ifdef CONFIG_SMP /* diff --git a/kernel/timer.c b/kernel/timer.c index 9062a82ee8ec..6b812c04737b 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -825,7 +825,7 @@ void update_process_times(int user_tick) */ static unsigned long count_active_tasks(void) { - return (nr_running() + nr_uninterruptible()) * FIXED_1; + return nr_active() * FIXED_1; } /*