From db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d Mon Sep 17 00:00:00 2001 From: Jack Steiner Date: Fri, 31 Mar 2006 02:31:21 -0800 Subject: [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 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/sched.h b/include/linux/sched.h index d04186d8cc6..ab84adf5bb9 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 -- cgit v1.2.3