From: Willy Tarreau <w@1wt.eu>
Date: Sat, 10 Apr 2021 23:18:39 +0000 (+0200)
Subject: MINOR: freq_ctr: add cpu_relax in the rotation loop of update_freq_ctr_period()
X-Git-Tag: v2.4-dev17~143
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6339c19cacb2010d2bf71066e436f5cc27252746;p=thirdparty%2Fhaproxy.git

MINOR: freq_ctr: add cpu_relax in the rotation loop of update_freq_ctr_period()

When counters are rotated, there is contention between the threads which
can slow down the operation of the thread performing the rotation. Let's
apply a cpu_relax there to let the first thread finish faster.
---

diff --git a/include/haproxy/freq_ctr.h b/include/haproxy/freq_ctr.h
index 9c10038a32..6b0cebff16 100644
--- a/include/haproxy/freq_ctr.h
+++ b/include/haproxy/freq_ctr.h
@@ -50,7 +50,7 @@ static inline unsigned int update_freq_ctr_period(struct freq_ctr *ctr,
 
 		/* remove the bit, used for the lock */
 		curr_tick &= ~1;
-	} while (!_HA_ATOMIC_CAS(&ctr->curr_tick, &curr_tick, curr_tick | 0x1));
+	} while (!_HA_ATOMIC_CAS(&ctr->curr_tick, &curr_tick, curr_tick | 0x1) && __ha_cpu_relax());
 	__ha_barrier_atomic_store();
 
 	if (now_ms_tmp - curr_tick >= period) {