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"' 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 --- kernel/sched.c | 33 +++++++++++++++++++++++++++++++-- kernel/sched_fair.c | 17 +++++++++++++---- 2 files changed, 44 insertions(+), 6 deletions(-) Index: tip/kernel/sched.c =================================================================== --- tip.orig/kernel/sched.c +++ tip/kernel/sched.c @@ -71,6 +71,7 @@ #include #include #include +#include #include #include @@ -502,7 +503,32 @@ static void destroy_cfs_bandwidth(struct 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) {} @@ -9188,7 +9214,7 @@ static int __cfs_schedulable(struct task 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) @@ -9216,6 +9242,9 @@ static int tg_set_cfs_bandwidth(struct t 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; Index: tip/kernel/sched_fair.c =================================================================== --- tip.orig/kernel/sched_fair.c +++ tip/kernel/sched_fair.c @@ -1408,7 +1408,7 @@ static void __account_cfs_rq_runtime(str 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); @@ -1416,13 +1416,13 @@ static __always_inline void account_cfs_ 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; } /* @@ -1743,6 +1743,9 @@ static void __return_cfs_rq_runtime(stru 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; @@ -1788,6 +1791,9 @@ static void do_sched_cfs_slack_timer(str */ 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; @@ -1805,6 +1811,9 @@ static void check_enqueue_throttle(struc /* 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/