From: Victor Julien <vjulien@oisf.net>
Date: Wed, 18 Sep 2024 09:50:59 +0000 (+0200)
Subject: threads: align struct to CLS to avoid false sharing
X-Git-Tag: suricata-8.0.0-beta1~585
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2af67e17bc7c3e142abee2957d5597b5d55ea4f8;p=thirdparty%2Fsuricata.git

threads: align struct to CLS to avoid false sharing

Since `Thread` objects are part of a big allocation, more than one
Thread could be on a single cache line, leading to false sharing. Atomic
updates to one `Thread` could then lead to poor performance accessing
another `Thread`. Align to CLS (cache line size) to avoid this.
---

diff --git a/src/tm-threads.c b/src/tm-threads.c
index 42200dbd43..5da183c311 100644
--- a/src/tm-threads.c
+++ b/src/tm-threads.c
@@ -2064,6 +2064,7 @@ static void TmThreadDumpThreads(void)
 }
 #endif
 
+/* Aligned to CLS to avoid false sharing between atomic ops. */
 typedef struct Thread_ {
     ThreadVars *tv;     /**< threadvars structure */
     const char *name;
@@ -2075,7 +2076,7 @@ typedef struct Thread_ {
     SCTime_t sys_sec_stamp; /**< timestamp in real system
                              *   time when the pktts was last updated. */
     SCSpinlock spin;
-} Thread;
+} __attribute__((aligned(CLS))) Thread;
 
 typedef struct Threads_ {
     Thread *threads;