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

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Date: Tue, 27 Feb 2024 09:36:22 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Marcelo Tosatti <mtosatti@...hat.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, 
	Frederic Weisbecker
	 <frederic@...nel.org>, Valentin Schneider <vschneid@...hat.com>, Willem de
	Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next] net/core/dev.c: enable timestamp static key if
 CPU isolation is configured

Hi,

On Thu, 2024-02-22 at 15:27 -0300, Marcelo Tosatti 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.

I believe Willem is correct, the relevant flag is
SOF_TIMESTAMPING_RX_SOFTWARE, see:

https://elixir.bootlin.com/linux/v6.8-rc5/source/net/core/sock.c#L938

the example you used is a sort of API misuse, placing flag where a bool
is expected. 

Please send a v2 with the updated commit message, you can mention both
SO_TIMESTAMPING (SOF_TIMESTAMPING_RX_SOFTWARE) and SO_TIMESTAMP.

Please also include Willem in recipients list, since he gave feedback
on previous version.

Thanks!

Paolo