2024-02-22 19:00:44

by Marcelo Tosatti

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

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.

So enable the static key unconditionally, if CPU isolation is enabled,
thus avoiding the IPIs.

Signed-off-by: Marcelo Tosatti <[email protected]>

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);

2024-02-27 08:37:12

by Paolo Abeni

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