linux-kernel - Re: [PATCH] net/core/dev.c: enable timestamp static key if CPU isolation is configured

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Date: Fri, 16 Feb 2024 16:13:36 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Marcelo Tosatti <mtosatti@...hat.com>
Cc: linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>, 
	Frederic Weisbecker <frederic@...nel.org>, Valentin Schneider <vschneid@...hat.com>, 
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net/core/dev.c: enable timestamp static key if CPU
 isolation is configured

On Fri, Feb 16, 2024 at 4:02 PM Marcelo Tosatti <mtosatti@...hat.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@...hat.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.