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

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

[Marcelo Tosatti]

For systems that use CPU isolation (via nohz_full), creating or destroying
a socket with timestamping (SOCK_TIMESTAMPING_RX_SOFTWARE) 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>

---                                                                                                                                         
v2: mention SOF_TIMESTAMPING_OPT_TX_SWHW in the commit log (Willem de Bruijn / Paolo Abeni)
v3: SOF_TIMESTAMPING_OPT_TX_SWHW is irrelevant (Willem de Bruijn)

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);

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

[Willem de Bruijn]

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@redhat.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?

Aside from that small question LGTM.

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

[Willem de Bruijn]

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@redhat.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?

You sent a v4, but can you answer this question?