Re: [PATCH v7 net-next] net: hyperv: dump TX indirection table to ethtool regs

On Thu, Jul 23, 2020 at 07:55:20PM +0000, Haiyang Zhang wrote:

quoted

-----Original Message-----
From: Michal Kubecek <redacted>
Sent: Thursday, July 23, 2020 3:36 PM
To: Chi Song <redacted>
Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
[off-list ref]; Stephen Hemminger [off-list ref];
Wei Liu [off-list ref]; David S. Miller [off-list ref]; Jakub
Kicinski [off-list ref]; linux-hyperv@vger.kernel.org;
netdev@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 net-next] net: hyperv: dump TX indirection table to
ethtool regs

On Wed, Jul 22, 2020 at 11:59:09PM -0700, Chi Song wrote:

quoted

An imbalanced TX indirection table causes netvsc to have low
performance. This table is created and managed during runtime. To help
better diagnose performance issues caused by imbalanced tables, it needs
make TX indirection tables visible.

Because TX indirection table is driver specified information, so
display it via ethtool register dump.

Is the Tx indirection table really unique to netvsc or can we expect
other drivers to support similar feature? Also, would it make sense to
allow also setting the table with ethtool? (AFAICS it can be only set
from hypervisor at the moment.)

Currently, TX indirection table is only used by the Hyper-V synthetic NIC. I'm 
not aware of any other NIC planning to use this.
This table is created by host dynamically based on host side CPU usage, 
and provided to the VM periodically. Our protocol doesn't let the guest side 
to change it.

If host is expected to rewrite the table periodically, it would indeed
be of little use to set it on guest side. OK, let's do it as register
dump and see if someone else comes with similar feature.

Michal