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

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.

Signed-off-by: Chi Song <chisong@microsoft.com>
---
v7: move to ethtool register dump
v6: update names to be more precise, remove useless assignment
v5: update variable orders
v4: use a separated group to organize tx_indirection better, change
 location of attributes init/exit to netvsc_drv_init/exit

 drivers/net/hyperv/netvsc_drv.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

 {
 	struct net_device_context *ndev_ctx = netdev_priv(ndev);
@@ -1950,6 +1967,8 @@ static void netvsc_set_msglevel(struct net_device
*ndev, u32 val)

 static const struct ethtool_ops ethtool_ops = {
 	.get_drvinfo	= netvsc_get_drvinfo,
+	.get_regs_len	= netvsc_get_regs_len,
+	.get_regs	= netvsc_get_regs,
 	.get_msglevel	= netvsc_get_msglevel,
 	.set_msglevel	= netvsc_set_msglevel,
 	.get_link	= ethtool_op_get_link,

On Wed, 22 Jul 2020 23:59:09 -0700 (PDT) Chi Song wrote:
> 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.
> 
> Signed-off-by: Chi Song <chisong@microsoft.com>

The patch looks good to me, but it has been corrupted by your email
client, could you perhaps try git send-email?

> +	memcpy(regs_buff, ndc->tx_table, VRSS_SEND_TAB_SIZE *
> sizeof(u32));

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

It kind of feels that the actual reason for using register dump was that
it's there and it was easy to use rather than that the information would
logically belong there. We already have a specific interface for getting
and seting receive indirection table; perhaps it would make sense to
have also one for the transmit indirection table.

Michal

> -----Original Message-----
> From: Michal Kubecek <mkubecek@suse.cz>
> Sent: Thursday, July 23, 2020 3:36 PM
> To: Chi Song <Song.Chi@microsoft.com>
> Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> Wei Liu <wei.liu@kernel.org>; David S. Miller <davem@davemloft.net>; Jakub
> Kicinski <kuba@kernel.org>; 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:
> > 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.

Thanks,
- Haiyang

On Thu, Jul 23, 2020 at 07:55:20PM +0000, Haiyang Zhang wrote:
> > -----Original Message-----
> > From: Michal Kubecek <mkubecek@suse.cz>
> > Sent: Thursday, July 23, 2020 3:36 PM
> > To: Chi Song <Song.Chi@microsoft.com>
> > Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> > <haiyangz@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> > Wei Liu <wei.liu@kernel.org>; David S. Miller <davem@davemloft.net>; Jakub
> > Kicinski <kuba@kernel.org>; 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:
> > > 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