[ipxe-devel] [PATCH] [dhcp] Call cpu_nap() to avoid high CPU load in the dhcp client

[Bernhard Kohl]

This is especially important in virtual machines as waiting
for responses from the server, if it is temporarily not
available, causes 100% CPU load on one of the host's cores.
This happens a lot if all machines including the dhcp server
are running in VMs.

Signed-off-by: Bernhard Kohl <bernhard.kohl at nsn.com>
---
 src/net/udp/dhcp.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/src/net/udp/dhcp.c b/src/net/udp/dhcp.c
index e63c3e4..7bdab39 100644
--- a/src/net/udp/dhcp.c
+++ b/src/net/udp/dhcp.c
@@ -44,6 +44,8 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/dhcppkt.h>
 #include <ipxe/dhcp_arch.h>
 #include <ipxe/features.h>
+#include <ipxe/process.h>
+#include <ipxe/nap.h>
 
 /** @file
  *
@@ -241,6 +243,9 @@ struct dhcp_session {
 	unsigned int count;
 	/** Start time of the current state (in ticks) */
 	unsigned long start;
+
+	/** Process */
+	struct process process;
 };
 
 /**
@@ -268,6 +273,9 @@ static void dhcp_finished ( struct dhcp_session *dhcp, int rc ) {
 	/* Stop retry timer */
 	stop_timer ( &dhcp->timer );
 
+	/* Stop process */
+	process_del ( &dhcp->process );
+
 	/* Shut down interfaces */
 	intf_shutdown ( &dhcp->xfer, rc );
 	intf_shutdown ( &dhcp->job, rc );
@@ -1247,6 +1255,15 @@ static void dhcp_timer_expired ( struct retry_timer *timer, int fail ) {
 	dhcp->state->expired ( dhcp );
 }
 
+/**
+ * DHCP process
+ *
+ * @v dhcp		DHCP session
+ */
+static void dhcp_step ( struct dhcp_session *dhcp __unused) {
+	cpu_nap();
+}
+
 /****************************************************************************
  *
  * Job control interface
@@ -1262,6 +1279,10 @@ static struct interface_operation dhcp_job_op[] = {
 static struct interface_descriptor dhcp_job_desc =
 	INTF_DESC ( struct dhcp_session, job, dhcp_job_op );
 
+/** DHCP process descriptor */
+static struct process_descriptor dhcp_process_desc =
+	PROC_DESC ( struct dhcp_session, process, dhcp_step );
+
 /****************************************************************************
  *
  * Instantiators
@@ -1319,6 +1340,7 @@ int start_dhcp ( struct interface *job, struct net_device *netdev ) {
 	intf_init ( &dhcp->job, &dhcp_job_desc, &dhcp->refcnt );
 	intf_init ( &dhcp->xfer, &dhcp_xfer_desc, &dhcp->refcnt );
 	timer_init ( &dhcp->timer, dhcp_timer_expired, &dhcp->refcnt );
+	process_init ( &dhcp->process, &dhcp_process_desc, &dhcp->refcnt );
 	dhcp->netdev = netdev_get ( netdev );
 	dhcp->local.sin_family = AF_INET;
 	dhcp->local.sin_port = htons ( BOOTPC_PORT );
-- 
1.7.7.6