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 <mtosatti@redhat.com>

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);

On Fri, Feb 16, 2024 at 4:02 PM Marcelo Tosatti <mtosatti@redhat.com> wrote:
>
>
> 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 <mtosatti@redhat.com>
>
> 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);
>

CC netdev@

SGTM, but could you please add netdev@ when sending patches for network trees ?

Thanks.