From: Willy Tarreau <w@1wt.eu>
Date: Mon, 18 Jun 2012 18:01:30 +0000 (+0200)
Subject: OPTIM: i386: make use of kernel-mode-linux when available
X-Git-Tag: v1.5-dev12~136
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5b88da269c528a399606f35cf13e7dea58eabd90;p=thirdparty%2Fhaproxy.git

OPTIM: i386: make use of kernel-mode-linux when available

If haproxy is built with support for USE_VSYSCALL_DLSYM, it's very
easy to check for KML availability. So let's enable it. Tests show
a small overall performance improvement around 1%. Other tests show
that the syscall overhead is divided by 4 on a Geode LX using this
method.
---

diff --git a/src/i386-linux-vsys.c b/src/i386-linux-vsys.c
index a4927e2d20..1bdd9e9d7c 100644
--- a/src/i386-linux-vsys.c
+++ b/src/i386-linux-vsys.c
@@ -184,10 +184,14 @@ static void __i386_linux_vsyscall_init(void)
 #ifdef USE_VSYSCALL_DLSYM
 	void *handle = dlopen("linux-gate.so.1", RTLD_NOW);
 	if (handle) {
-		void *ptr = dlsym(handle, "__kernel_vsyscall");
-		dlclose(handle);
+		void *ptr;
+
+		ptr = dlsym(handle, "__kernel_vsyscall_kml");
+		if (!ptr)
+			ptr = dlsym(handle, "__kernel_vsyscall");
 		if (ptr)
 			vsyscall = ptr;
+		dlclose(handle);
 	}
 #else
 	/* Heuristic: trying to mprotect() the VDSO area will only succeed if