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| author | Jack Steiner <steiner@sgi.com> | 2006-03-31 02:31:21 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-03-31 12:18:58 -0800 |
| commit | db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d (patch) | |
| tree | ad8e68882f7c36216e16ab264101c5da96ccd5c9 /kernel | |
| parent | 3055addadbe9bfb2365006a1c13fd342a8d30d52 (diff) | |
| download | lwn-db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d.tar.gz lwn-db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d.zip | |
[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 <steiner@sgi.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched.c | 15 | ||||
| -rw-r--r-- | kernel/timer.c | 2 |
2 files changed, 16 insertions, 1 deletions
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; } /* |