linux-kernel - Re: [PATCH net-next -v3] net/core/dev.c: enable timestamp static key if CPU isolation is configured

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Date: Thu, 07 Mar 2024 04:07:17 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 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 net-next -v3] net/core/dev.c: enable timestamp static key
 if CPU isolation is configured

Willem de Bruijn wrote:
> Marcelo Tosatti wrote:
> > 
> > For systems that use CPU isolation (via nohz_full), creating or destroying
> > a socket with
> 
> - timestamping (SOCK_TIMESTAMPING_RX_SOFTWARE) might cause a
> + 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>
> 
> > 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);
> > 
> 
> Can this be included in the existing net_dev_init
> subsys_initcall?

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