From: Eric Biggers <ebiggers3@gmail.com>
Date: Fri, 31 Jan 2014 21:07:59 +0000 (-0600)
Subject: lz_sarray:  Prefetch portion of suffix array to be searched
X-Git-Tag: v1.6.2~33
X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=fc897414e8b4ba34794d3179428a56773f45e9a3

lz_sarray:  Prefetch portion of suffix array to be searched

Seems to improve performance of LZX and LZMS compression on large chunks
by ~5%.  Results may vary.
---

diff --git a/include/wimlib/compiler.h b/include/wimlib/compiler.h
index d32d092b..21fabd99 100644
--- a/include/wimlib/compiler.h
+++ b/include/wimlib/compiler.h
@@ -22,6 +22,7 @@
 #	define likely(x) __builtin_expect(!!(x), 1)
 #	define unlikely(x) __builtin_expect(!!(x), 0)
 #	define inline inline __attribute__((always_inline))
+#	define prefetch(x) __builtin_prefetch(x)
 #else
 #	define WIMLIBAPI
 #	define _always_inline_attribute inline
@@ -33,6 +34,7 @@
 #	define _aligned_attribute(size)
 #	define likely(x) (x)
 #	define unlikely(x) (x)
+#	define prefetch(x)
 #endif /* __GNUC__ */
 
 #endif /* _WIMLIB_COMPILER_H */
diff --git a/include/wimlib/lz_sarray.h b/include/wimlib/lz_sarray.h
index 5b63ae7c..30dc2b30 100644
--- a/include/wimlib/lz_sarray.h
+++ b/include/wimlib/lz_sarray.h
@@ -34,7 +34,8 @@
 #ifndef _WIMLIB_LZ_SARRAY_H
 #define _WIMLIB_LZ_SARRAY_H
 
-#include "wimlib/compiler.h" /* must define '_always_inline_attribute'  */
+#include "wimlib/compiler.h" /* must define '_always_inline_attribute',
+				'likely()', and 'prefetch()'.  */
 #include "wimlib/lz.h"       /* must define 'struct raw_match' and LZ_ASSERT()  */
 #include "wimlib/types.h"    /* must define 'bool', 'u8', 'u16, and 'u32'  */
 
@@ -285,6 +286,19 @@ lz_sarray_get_matches(struct lz_sarray *mf,
 	/* Prepare for searching the current position.  */
 	lz_sarray_update_salink(r, link);
 
+#if 1
+	/* Prefetch next position in SA and link.
+	 *
+	 * This can improve performance on large windows since the locations in
+	 * SA and link at which each successive search begins are in general
+	 * randomly distributed.  */
+	if (likely(i + 1 < mf->window_size)) {
+		const lz_sarray_pos_t next_r = ISA[i + 1];
+		prefetch(&SA[next_r]);
+		prefetch(&link[next_r]);
+	}
+#endif
+
 	/* L = rank of next suffix to the left;
 	 * R = rank of next suffix to the right;
 	 * lenL = length of match between current position and the suffix with rank L;