gve: Cache link_speed value from device

[ Upstream commit 68c3e4fc8628b1487c965aabb29207249657eb5f ]

The link speed is never changed for the uptime of a VM, and the current
implementation sends an admin queue command for each call. Admin queue
command invocations have nontrivial overhead (e.g., VM exits), which can
be disruptive to users if triggered frequently. Our telemetry data shows
that there are VMs that make frequent calls to this admin queue command.
Caching the result of the original admin queue command would eliminate
the need to send multiple admin queue commands on subsequent calls to
retrieve link speed.

Fixes: 7e074d5a76ca ("gve: Enable Link Speed Reporting in the driver.")
Signed-off-by: Joshua Washington <joshwash@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230321172332.91678-1-joshwash@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/ethernet/google/gve/gve_ethtool.c b/drivers/net/ethernet/google/gve/gve_ethtool.c
index 7b9a2d9d962436d8c99301669768356e90bdb4f7..38df602f2869c74a64ecd8463662373e2f013f98 100644 (file)
--- a/drivers/net/ethernet/google/gve/gve_ethtool.c
+++ b/drivers/net/ethernet/google/gve/gve_ethtool.c
@@ -535,7 +535,10 @@ static int gve_get_link_ksettings(struct net_device *netdev,
                                  struct ethtool_link_ksettings *cmd)
 {
        struct gve_priv *priv = netdev_priv(netdev);
-       int err = gve_adminq_report_link_speed(priv);
+       int err = 0;
+
+       if (priv->link_speed == 0)
+               err = gve_adminq_report_link_speed(priv);
 
        cmd->base.speed = priv->link_speed;
        return err;