[PATCH] locking/local_lock: Reduce local_[un]lock_nested_bh() overhead

[Eric Dumazet <edumazet@google.com>]

On !PREEMPT_RT and !LOCKDEP kernels, local_[un]lock_nested_bh()
are supposed to be NOP.

This is not exactly true after 7ff495e26a39 ("local_lock: Move
this_cpu_ptr() notation from internal to main header") due to
this_cpu_ptr() being evaluated even if its result it not used.

This prevents some tail call optimizations.

After this patch we have gains in networking fast paths:

$ scripts/bloat-o-meter -t vmlinux.0 vmlinux
add/remove: 0/0 grow/shrink: 0/36 up/down: 0/-644 (-644)
Function                                     old     new   delta
tcp_sigpool_end                               79      71      -8
skb_attempt_defer_free                       457     449      -8
ppp_xmit_process                             179     171      -8
ppp_write                                    411     403      -8
ppp_output_wakeup                            135     127      -8
napi_skb_cache_get_bulk                      440     432      -8
napi_consume_skb                             409     401      -8
dst_cache_set_ip6                            203     195      -8
dst_cache_set_ip4                            135     127      -8
cpu_map_enqueue                              193     185      -8
bq_enqueue                                   263     255      -8
__netdev_alloc_skb                           377     369      -8
__netdev_alloc_frag_align                    155     147      -8
__napi_kfree_skb                             136     128      -8
napi_skb_free_stolen_head                    199     190      -9
input_action_end_bpf                        1083    1072     -11
napi_alloc_skb                               275     263     -12
__napi_alloc_frag_align                       59      45     -14
xdp_build_skb_from_zc                        590     574     -16
tcp_v4_send_ack                             1129    1113     -16
sch_frag_xmit_hook                          1260    1244     -16
flush_backlog                                507     491     -16
dst_cache_get_ip6                             99      83     -16
dst_cache_get_ip4                             90      74     -16
do_xdp_generic                               932     916     -16
__napi_build_skb                             591     575     -16
__dev_flush                                  115      99     -16
__cpu_map_flush                               85      69     -16
dst_cache_get                                 55      38     -17
tcp_v4_send_reset                           2682    2658     -24
mptcp_subflow_delegate                       955     931     -24
__alloc_skb                                  988     964     -24
mptcp_napi_poll                              310     281     -29
nat_keepalive_work_single                   1385    1335     -50
gro_cells_receive                            320     244     -76
process_backlog                              486     404     -82
Total: Before=25812320, After=25811676, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Marco Elver <elver@google.com>
---
 include/linux/local_lock.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index b8830148a8591c17c22e36470fbc13ff5c354955..40c2da54a0b720265be7b6327e0922a49befd8fc 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -94,12 +94,19 @@ DEFINE_LOCK_GUARD_1(local_lock_irqsave, local_lock_t __percpu,
 		    local_unlock_irqrestore(_T->lock, _T->flags),
 		    unsigned long flags)
 
+#if defined(WARN_CONTEXT_ANALYSIS) || defined(CONFIG_PREEMPT_RT) || \
+    defined(CONFIG_DEBUG_LOCK_ALLOC)
 #define local_lock_nested_bh(_lock)				\
 	__local_lock_nested_bh(__this_cpu_local_lock(_lock))
 
 #define local_unlock_nested_bh(_lock)				\
 	__local_unlock_nested_bh(__this_cpu_local_lock(_lock))
 
+#else
+static inline void local_lock_nested_bh(local_lock_t *_lock) {}
+static inline void local_unlock_nested_bh(local_lock_t *__lock) {}
+#endif
+
 DEFINE_LOCK_GUARD_1(local_lock_nested_bh, local_lock_t __percpu,
 		    local_lock_nested_bh(_T->lock),
 		    local_unlock_nested_bh(_T->lock))

base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
prerequisite-patch-id: f6002c357582927a383603a22e69bc0d7a5b9528
-- 
2.53.0.473.g4a7958ca14-goog