From 7f03c419bc9bec268998c2d2154c0d133a8a6bbc Mon Sep 17 00:00:00 2001
From: Maxim Sobolev <sobomax@FreeBSD.org>
Date: Mon, 27 Oct 2008 06:25:02 +0000
Subject: [PATCH] Default HZ value (1,000) on i386/amd64 is not very virtual
 machine friendly. Due to the nature of the beast it causes lot of
 unproductive overhead. This is especially bad when running SMP kernel on
 VMWare with several virtual processors - idle FreeBSD guest with SMP kernel
 takes 150% host CPU time on my dual-core MacBook Pro when I am enabling two
 virtual CPUs, making even host not very usable. Detect when we are running in
 the sandbox and reduce HZ to 10 (can be adjusted via VM_HZ in the kernel
 config) in such cases. This brings host CPU usage of idle FreeBSD/SMP on two
 virtual processors down to 10%.

Detect most popular VM platforms out there - VMWare, Parallels, VirtualBox
and VirtualPC.

MFC after:	2 weeks
---
 sys/kern/subr_param.c | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/sys/kern/subr_param.c b/sys/kern/subr_param.c
index 89150acf2cd8..138ccbc67982 100644
--- a/sys/kern/subr_param.c
+++ b/sys/kern/subr_param.c
@@ -57,6 +57,13 @@ __FBSDID("$FreeBSD$");
 #  else
 #    define	HZ 100
 #  endif
+#  ifndef HZ_VM
+#    define	HZ_VM 10
+#  endif
+#else
+#  ifndef HZ_VM
+#    define	HZ_VM HZ
+#  endif
 #endif
 #define	NPROC (20 + 16 * maxusers)
 #ifndef NBUF
@@ -111,6 +118,30 @@ SYSCTL_ULONG(_kern, OID_AUTO, sgrowsiz, CTLFLAG_RDTUN, &sgrowsiz, 0,
  */
 struct	buf *swbuf;
 
+char *vm_pnames[] = {
+	"VMware Virtual Platform",	/* VMWare VM */
+	"Virtual Machine",		/* Microsoft VirtualPC */
+	"VirtualBox",			/* Sun xVM VirtualBox */
+	"Parallels Virtual Platform",	/* Parallels VM */
+	NULL
+};
+
+static int
+detect_virtual(void)
+{
+	char *sysenv;
+	int i;
+
+	sysenv = getenv("smbios.system.product");
+	if (sysenv != NULL) {
+		for (i = 0; vm_pnames[i] != NULL; i++) {
+			if (strcmp(sysenv, vm_pnames[i]) == 0)
+				return 1;
+		}
+	}
+	return 0;
+}
+
 /*
  * Boot time overrides that are not scaled against main memory
  */
@@ -118,8 +149,15 @@ void
 init_param1(void)
 {
 
-	hz = HZ;
+	hz = -1;
 	TUNABLE_INT_FETCH("kern.hz", &hz);
+	if (hz == -1) {
+		if (detect_virtual()) {
+			hz = HZ_VM;
+		} else {
+			hz = HZ;
+		}
+	}
 	tick = 1000000 / hz;
 
 #ifdef VM_SWZONE_SIZE_MAX