From: Willy Tarreau <w@1wt.eu>
Date: Tue, 12 Jun 2012 07:16:56 +0000 (+0200)
Subject: OPTIM: halog: improve cold-cache behaviour when loading a file
X-Git-Tag: v1.5-dev12~141
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=f8c95d2a25b5b0ff4c8d50c57e4ac6195dcd82f6;p=thirdparty%2Fhaproxy.git

OPTIM: halog: improve cold-cache behaviour when loading a file

Using posix_fadvise() it is possible to tell the system that we're
going to read a whole file at once. The kernel then doubles the
read-ahead size for this file. On Linux with an SSD, this has improved
cold-cache performance by around 20%. Hot-cache is not affected at all.
---

diff --git a/contrib/halog/halog.c b/contrib/halog/halog.c
index 250623d827..448e5c0a83 100644
--- a/contrib/halog/halog.c
+++ b/contrib/halog/halog.c
@@ -672,6 +672,15 @@ int main(int argc, char **argv)
 	else if (filter & FILT_COUNT_ONLY)
 		line_filter = NULL;
 
+#if defined(POSIX_FADV_SEQUENTIAL)
+	/* around 20% performance improvement is observed on Linux with this
+	 * on cold-cache. Surprizingly, WILLNEED is less performant. Don't
+	 * use NOREUSE as it flushes the cache and prevents easy data
+	 * manipulation on logs!
+	 */
+	posix_fadvise(0, 0, 0, POSIX_FADV_SEQUENTIAL);
+#endif
+
 	if (!line_filter &&
 	    !(filter & (FILT_HTTP_ONLY|FILT_TIME_RESP|FILT_ERRORS_ONLY|FILT_HTTP_STATUS|FILT_QUEUE_ONLY|FILT_QUEUE_SRV_ONLY|FILT_TERM_CODE_NAME))) {
 		/* read the whole file at once first */