kernel: Add __cacheline_aligned macro

This commit introduces a "__cacheline_aligned" macro which aligns data
by the cache line size (COHERENCY_UNIT bytes). This is useful for
heavily contended locks.

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 22 insertions, 0 deletions

diff --git a/sys/include/sys/cdefs.h b/sys/include/sys/cdefs.h
index fc21750..655a023 100644
--- a/sys/include/sys/cdefs.h
+++ b/sys/include/sys/cdefs.h
@@ -30,10 +30,27 @@
 #ifndef _SYS_CDEFS_H_
 #define _SYS_CDEFS_H_
 
+#include <sys/param.h>
+
 #define __ASMV          __asm__ __volatile__
 #define __always_inline __attribute__((__always_inline__))
 #define __packed        __attribute__((__packed__))
 #define __likely(exp)   __builtin_expect(((exp) != 0), 1)
 #define __unlikely(exp) __builtin_expect(((exp) != 0), 0)
 
+#if defined(_KERNEL)
+/*
+ *  Align data on a cache line boundary. This is
+ *  mostly useful for certain locks to ensure they
+ *  have their own cache line to reduce contention.
+ *
+ */
+#ifndef __cacheline_aligned
+#define __cacheline_aligned                             \
+    __attribute__((__aligned__(COHERENCY_UNIT),         \
+                __section__(".data.cacheline_aligned")))
+
+#endif  /* __cacheline_aligned */
+#endif  /* _KERNEL */
+
 #endif  /* !_SYS_CDEFS_H_ */
diff --git a/sys/include/sys/param.h b/sys/include/sys/param.h
index a35a094..483dc15 100644
--- a/sys/include/sys/param.h
+++ b/sys/include/sys/param.h
@@ -30,6 +30,11 @@
 #ifndef _SYS_PARAM_H_
 #define _SYS_PARAM_H_
 
+/* Assumed cache line size */
+#ifndef COHERENCY_UNIT
+#define COHERENCY_UNIT 64
+#endif
+
 /* Bit related macros */
 #define ISSET(v, f)  ((v) & (f))
 #define BIT(n) (1 << (n))