[PATCH net] gve: Cache link_speed value from device

[PATCH net] gve: Cache link_speed value from device

[joshwash]

From: Joshua Washington <joshwash@google.com>

The link speed is never changed for the uptime of a VM. Caching the
value will allow for better performance.

Fixes: 7e074d5a76ca ("gve: Enable Link Speed Reporting in the driver.")
Signed-off-by: Joshua Washington <joshwash@google.com>
---
 google/gve/gve_ethtool.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/google/gve/gve_ethtool.c b/google/gve/gve_ethtool.c
index b18804e..cfd4b8d 100644
--- a/google/gve/gve_ethtool.c
+++ b/google/gve/gve_ethtool.c
@@ -584,7 +584,10 @@ 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;
-- 
2.40.0.rc1.284.g88254d51c5-goog

Re: [PATCH net] gve: Cache link_speed value from device

[Jakub Kicinski]

On Wed, 15 Mar 2023 10:40:16 -0700 joshwash@google.com wrote:
> From: Joshua Washington <joshwash@google.com>
> 
> The link speed is never changed for the uptime of a VM. Caching the
> value will allow for better performance.
> 
> Fixes: 7e074d5a76ca ("gve: Enable Link Speed Reporting in the driver.")

If it needs to go in as a fix / to stable we need a bit more info about
the nature of the problem. What user-visible (or hypervisor-visible)
impact will be?  What entity needs link info so often that it becomes
a problem?

The code looks fine as an optimization, i.e. for net-next, but you say
"PATCH net" and there's a Fixes tag...

Re: [PATCH net] gve: Cache link_speed value from device

[Jakub Kicinski]

On Thu, 16 Mar 2023 17:42:27 -0700 Jakub Kicinski wrote:
> If it needs to go in as a fix / to stable we need a bit more info about
> the nature of the problem. What user-visible (or hypervisor-visible)
> impact will be?  What entity needs link info so often that it becomes
> a problem?
> 
> The code looks fine as an optimization, i.e. for net-next, but you say
> "PATCH net" and there's a Fixes tag...

Hm, actually it doesn't apply to either tree..