[PATCH net-next -v6] net: enable timestamp static key if CPU isolation is configured

[PATCH net-next -v6] net: 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 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>

---
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)
v4: additional changelog improvements (Willem de Bruijn)
v5: late initcall not necessary, can use subsys initcall (Willem de Bruijn)
v6: rebase against net-next, change subject (Jakub Kicinski)

diff --git a/net/core/dev.c b/net/core/dev.c
index 5d36a634f468..48c725caa130 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -157,6 +157,7 @@
 #include <net/page_pool/types.h>
 #include <net/page_pool/helpers.h>
 #include <net/rps.h>
+#include <linux/sched/isolation.h>
 
 #include "dev.h"
 #include "net-sysfs.h"
@@ -11890,6 +11891,10 @@ static int __init net_dev_init(void)
 				       NULL, dev_cpu_dead);
 	WARN_ON(rc < 0);
 	rc = 0;
+
+	/* avoid static key IPIs to isolated CPUs */
+	if (housekeeping_enabled(HK_TYPE_MISC))
+		net_enable_timestamp();
 out:
 	if (rc < 0) {
 		for_each_possible_cpu(i) {

Re: [PATCH net-next -v6] net: 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 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>

Reviewed-by: Willem de Bruijn <willemb@google.com>

Re: [PATCH net-next -v6] net: enable timestamp static key if CPU isolation is configured

[Jakub Kicinski]

On Wed, 27 Mar 2024 21:02:13 -0300 Marcelo Tosatti wrote:
>  #include <net/page_pool/types.h>
>  #include <net/page_pool/helpers.h>
>  #include <net/rps.h>
> +#include <linux/sched/isolation.h>

Sorry for a late nit, could you put this include next to the other two
linux/sched* includes earlier in the file?
-- 
pw-bot: cr