netdev - [PATCH net-next -v4] net/core/dev.c: enable timestamp static key if CPU isolation is configured

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Message-ID: <ZejG+1YF4Rk89Gc9@tpad>
Date: Wed, 6 Mar 2024 16:41:47 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Valentin Schneider <vschneid@...hat.com>,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next -v4] net/core/dev.c: enable timestamp static key if
 CPU isolation is configured


For systems that use CPU isolation (via nohz_full), creating or destroying
a socket with SO_TIMESTAMP, SO_TIMESTAMPNS or SO_TIMESTAMPING with flag
SOF_TIMESTAMPING_RX_SOFTWARE will 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 <mtosatti@...hat.com>

---
v2: mention SOF_TIMESTAMPING_OPT_TX_SWHW in the commit log (Willem de Bruijn / Paolo Abeni)
v3: SOF_TIMESTAMPING_OPT_TX_SWHW is irrelevant (Willem de Bruijn)
v4: additional changelog improvements (Willem de Bruijn)

diff --git a/net/core/dev.c b/net/core/dev.c
index c588808be77f..15a32f5900e6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -155,6 +155,7 @@
 #include <net/netdev_rx_queue.h>
 #include <net/page_pool/types.h>
 #include <net/page_pool/helpers.h>
+#include <linux/sched/isolation.h>
 
 #include "dev.h"
 #include "net-sysfs.h"
@@ -11851,3 +11852,14 @@ 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);