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sched: Use jump labels to reduce overhead when bandwidth control is inactive 

Now that the linkage of jump-labels has been fixed they show a measurable
improvement in overhead for the enabled-but-unused case.

Workload is:

 'taskset -c 0 perf stat --repeat 50 -e instructions,cycles,branches
  bash -c "for ((i=0;i<5;i++)); do $(dirname $0)/pipe-test 20000; done"'

There's a speedup for all situations:

                 instructions            cycles                  branches
 -------------------------------------------------------------------------
 Intel Westmere
 base            806611770               745895590               146765378
 +jumplabel      803090165 (-0.44%)      713381840 (-4.36%)      144561130

 AMD Barcelona
 base            824657415               740055589               148855354
 +jumplabel      821056910 (-0.44%)      737558389 (-0.34%)      146635229

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111108042736.560831357@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul Turner 2011-11-07 20:26:33 -08:00 committed by Ingo Molnar
parent fccfdc6f0d
commit 56f570e512
2 changed files with 43 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
kernel/sched.c
View File

@ -72,6 +72,7 @@
#include <linux/ftrace.h>
#include <linux/slab.h>
#include <linux/init_task.h>
#include <linux/jump_label.h>
#include <asm/tlb.h>
#include <asm/irq_regs.h>
@ -503,7 +504,32 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
hrtimer_cancel(&cfs_b->period_timer);
hrtimer_cancel(&cfs_b->slack_timer);
}
#else
#ifdef HAVE_JUMP_LABEL
static struct jump_label_key __cfs_bandwidth_used;
static inline bool cfs_bandwidth_used(void)
{
return static_branch(&__cfs_bandwidth_used);
}
static void account_cfs_bandwidth_used(int enabled, int was_enabled)
{
/* only need to count groups transitioning between enabled/!enabled */
if (enabled && !was_enabled)
jump_label_inc(&__cfs_bandwidth_used);
else if (!enabled && was_enabled)
jump_label_dec(&__cfs_bandwidth_used);
}
#else /* !HAVE_JUMP_LABEL */
/* static_branch doesn't help unless supported */
static int cfs_bandwidth_used(void)
{
return 1;
}
static void account_cfs_bandwidth_used(int enabled, int was_enabled) {}
#endif /* HAVE_JUMP_LABEL */
#else /* !CONFIG_CFS_BANDWIDTH */
static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
static void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
@ -9203,7 +9229,7 @@ static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);
static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
{
int i, ret = 0, runtime_enabled;
int i, ret = 0, runtime_enabled, runtime_was_enabled;
struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
if (tg == &root_task_group)
@ -9231,6 +9257,9 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
goto out_unlock;
runtime_enabled = quota != RUNTIME_INF;
runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
account_cfs_bandwidth_used(runtime_enabled, runtime_was_enabled);
raw_spin_lock_irq(&cfs_b->lock);
cfs_b->period = ns_to_ktime(period);
cfs_b->quota = quota;

15
kernel/sched_fair.c
View File

@ -1421,7 +1421,7 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
static __always_inline void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
unsigned long delta_exec)
{
if (!cfs_rq->runtime_enabled)
if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
return;
__account_cfs_rq_runtime(cfs_rq, delta_exec);
@ -1429,13 +1429,13 @@ static __always_inline void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
return cfs_rq->throttled;
return cfs_bandwidth_used() && cfs_rq->throttled;
}
/* check whether cfs_rq, or any parent, is throttled */
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
return cfs_rq->throttle_count;
return cfs_bandwidth_used() && cfs_rq->throttle_count;
}
/*
@ -1756,6 +1756,9 @@ static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
if (!cfs_bandwidth_used())
return;
if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
return;
@ -1801,6 +1804,9 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
*/
static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
{
if (!cfs_bandwidth_used())
return;
/* an active group must be handled by the update_curr()->put() path */
if (!cfs_rq->runtime_enabled || cfs_rq->curr)
return;
@ -1818,6 +1824,9 @@ static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
/* conditionally throttle active cfs_rq's from put_prev_entity() */
static void check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
if (!cfs_bandwidth_used())
return;
if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
return;