Re: [PATCH v2] net: netvsc: Update default VMBus channels

[Erni Sri Satya Vennela]

On Thu, Aug 15, 2024 at 09:08:56AM -0700, Jakub Kicinski wrote:
> On Wed, 14 Aug 2024 09:59:13 -0700 Erni Sri Satya Vennela wrote:
> > Change VMBus channels macro (VRSS_CHANNEL_DEFAULT) in
> > Linux netvsc from 8 to 16 to align with Azure Windows VM
> > and improve networking throughput.
> > 
> > For VMs having less than 16 vCPUS, the channels depend
> > on number of vCPUs. Between 16 to 32 vCPUs, the channels
> > default to VRSS_CHANNEL_DEFAULT. For greater than 32 vCPUs,
> > set the channels to number of physical cores / 2 as a way
> > to optimize CPU resource utilization and scale for high-end
> > processors with many cores.
> > Maximum number of channels are by default set to 64.
> > 
> > Based on this change the subchannel creation would change as follows:
> > 
> > -------------------------------------------------------------
> > |No. of vCPU	|dev_info->num_chn	|subchannel created |
> > -------------------------------------------------------------
> > |  0-16		|	16		|	vCPU	    |
> > | >16 & <=32	|	16		|	16          |
> > | >32 & <=128	|	vCPU/2		|	vCPU/2      |
> > | >128		|	vCPU/2		|	64          |
> > -------------------------------------------------------------
> > 
> > Performance tests showed significant improvement in throughput:
> > - 0.54% for 16 vCPUs
> > - 0.83% for 32 vCPUs
> > - 1.76% for 48 vCPUs
> > - 10.35% for 64 vCPUs
> > - 13.47% for 96 vCPUs
> 
> Is there anything that needs clarifying in my feedback on v1?
> 
> https://lore.kernel.org/all/20240807201857.445f9f95@xxxxxxxxxx/
> 
> Ignoring maintainer feedback is known to result in angry outbursts.

I sincerely apologize for the miss on my part. I will make sure this
never happens again. As Haiyang mentioned, we were trying to use a
similar logic as in netif_get_num_default_rss_queues(), and trying to
make sure there are no potential regressions. I will work on Michael's
and  Haiyang's follow up comments. 
Please let us know your opinion on the same.