linux-kernel - Re: [PATCH -v2 net-next] net/core/dev.c: enable timestamp static key if CPU isolation is configured

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Date: Wed, 28 Feb 2024 10:32:56 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Marcelo Tosatti <mtosatti@...hat.com>, 
 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: Re: [PATCH -v2 net-next] net/core/dev.c: enable timestamp static key
 if CPU isolation is configured

Marcelo Tosatti wrote:
> 
> For systems that use CPU isolation (via nohz_full), creating or destroying
> a socket with timestamping (SOCK_TIMESTAMPING_RX_SOFTWARE and 
> SOF_TIMESTAMPING_OPT_TX_SWHW) might cause a

Again, SOF_TIMESTAMPING_OPT_TX_SWHW is irrelevant here.

See Documentation/networking/timestamping.rst for a definition of the
various flags.

> 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)

I did not suggest that

The subject line is slightly corrupted: net-next -v2

> 
> 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);
>