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]>

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]>

net/core/dev.c +12 -0

index 0d548431f3fa..cc9a77b4aa4e 100644
@@ -153,6 +153,7 @@
 #include <linux/prandom.h>
 #include <linux/once_lite.h>
 #include <net/netdev_rx_queue.h>
+#include <linux/sched/isolation.h>
 
 #include "dev.h"
 #include "net-sysfs.h"

@@ -11601,3 +11602,14 @@ 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);

Quoted 4 lines · Marcelo Tosatti

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.

This refers to SOF_TIMESTAMPING_RX_SOFTWARE, not SOF_TIMESTAMPING_OPT_TX_SWHW. See also sock_set_timestamping.

Quoted 8 lines · Willem de Bruijn

Quoted 4 lines · Marcelo Tosatti

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.

This refers to SOF_TIMESTAMPING_RX_SOFTWARE, not SOF_TIMESTAMPING_OPT_TX_SWHW. See also sock_set_timestamping.

Willem,

This test program does trigger the static key change:

int main (void)

{
        int option = SOF_TIMESTAMPING_OPT_TX_SWHW;
        int sock_fd;
        int ret;
        int pid_fd;
        pid_t pid;
        char buf[50];

...

        /* set the timestamping option
         * this is to trigger the IPIs that notify all cpus of the change
         */
        if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMP, &option, sizeof (option)) < 0) {
                printf("Could not enable timestamping option %x", (unsigned int)option);
                close(sock_fd);
                return 0;
        }

...