From: Willy Tarreau <w@1wt.eu>
Date: Thu, 11 Jun 2020 06:22:01 +0000 (+0200)
Subject: CLEANUP: compiler: add a THREAD_ALIGNED macro and use it where appropriate
X-Git-Tag: v2.2-dev9~7
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8e3f5c6661cdd6194110d724a025f0caa78596d7;p=thirdparty%2Fhaproxy.git

CLEANUP: compiler: add a THREAD_ALIGNED macro and use it where appropriate

Sometimes we need to align a struct member or a struct's size only when
threads are enabled. This is the case on fdtab for example. Instead of
using ugly ifdefs in the code itself, let's have a THREAD_ALIGNED() macro
performing the alignment only when threads are enabled. For now this was
only applied to fd-t.h as it was the only place found.
---

diff --git a/include/haproxy/compiler.h b/include/haproxy/compiler.h
index a0d4569856..0e594fa844 100644
--- a/include/haproxy/compiler.h
+++ b/include/haproxy/compiler.h
@@ -173,6 +173,17 @@
 #endif
 #endif
 
+/* sets alignment for current field or variable only when threads are enabled.
+ * Typically used to respect cache line alignment to avoid false sharing.
+ */
+#ifndef THREAD_ALIGNED
+#ifdef USE_THREAD
+#define THREAD_ALIGNED(x) __attribute__((aligned(x)))
+#else
+#define THREAD_ALIGNED(x)
+#endif
+#endif
+
 /* add a mandatory alignment for next fields in a structure */
 #ifndef ALWAYS_ALIGN
 #define ALWAYS_ALIGN(x)  union { } ALIGNED(x)
@@ -200,4 +211,16 @@
 #endif
 #endif
 
+/* add an optional alignment for next fields in a structure, only when threads
+ * are enabled. Typically used to respect cache line alignment to avoid false
+ * sharing.
+ */
+#ifndef THREAD_ALIGN
+#ifdef USE_THREAD
+#define THREAD_ALIGN(x) union { } ALIGNED(x)
+#else
+#define THREAD_ALIGN(x)
+#endif
+#endif
+
 #endif /* _HAPROXY_COMPILER_H */
diff --git a/include/haproxy/fd-t.h b/include/haproxy/fd-t.h
index 5f1c173aaa..1bffb26c44 100644
--- a/include/haproxy/fd-t.h
+++ b/include/haproxy/fd-t.h
@@ -114,7 +114,9 @@ struct fdlist {
 	int last;
 } ALIGNED(8);
 
-/* info about one given fd */
+/* info about one given fd. Note: only align on cache lines when using threads;
+ * 32-bit small archs can put everything in 32-bytes when threads are disabled.
+ */
 struct fdtab {
 	unsigned long running_mask;          /* mask of thread IDs currently using the fd */
 	unsigned long thread_mask;           /* mask of thread IDs authorized to process the fd */
@@ -127,14 +129,7 @@ struct fdtab {
 	unsigned char linger_risk:1;         /* 1 if we must kill lingering before closing */
 	unsigned char cloned:1;              /* 1 if a cloned socket, requires EPOLL_CTL_DEL on close */
 	unsigned char initialized:1;         /* 1 if init phase was done on this fd (e.g. set non-blocking) */
-}
-#ifdef USE_THREAD
-/* only align on cache lines when using threads; 32-bit small archs
- * can put everything in 32-bytes when threads are disabled.
- */
-ALIGNED(64)
-#endif
-;
+} THREAD_ALIGNED(64);
 
 /* polled mask, one bit per thread and per direction for each FD */
 struct polled_mask {