Subject: [PATCH] net/core/dev.c: enable timestamp static key if CPU isolation is configured

From: Marcelo Tosatti <[email-masked]>
Date: Tue, 20 Feb 2024 07:35:04 -0300

For systems that use CPU isolation (via nohz_full), creating or destroying
a socket with  timestamping (SOF_TIMESTAMPING_OPT_TX_SWHW) might cause a
static key to be enabled/disabled. This in turn causes undesired 
IPIs to isolated CPUs.

So enable the static key unconditionally, if CPU isolation is enabled,
thus avoiding the IPIs.

Signed-off-by: Marcelo Tosatti <[email-masked]>

diff --git a/net/core/dev.c b/net/core/dev.c
index 0d548431f3fa..cc9a77b4aa4e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -153,6 +153,7 @@
 #include <linux/prandom.h>
 #include <linux/once_lite.h>
 #include <net/netdev_rx_queue.h>
+#include <linux/sched/isolation.h>
 
 #include "dev.h"
 #include "net-sysfs.h"
@@ -11601,3 +11602,14 @@ static int __init net_dev_init(void)
 }
 
 subsys_initcall(net_dev_init);
+
+static int __init net_dev_late_init(void)
+{
+	/* avoid static key IPIs to isolated CPUs */
+	if (housekeeping_enabled(HK_TYPE_MISC))
+		net_enable_timestamp();
+
+	return 0;
+}
+
+late_initcall(net_dev_late_init);