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

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Message-ID: <20240815090856.7f8ec005@kernel.org>
Date: Thu, 15 Aug 2024 09:08:56 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Erni Sri Satya Vennela <ernis@...ux.microsoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, ernis@...rosoft.com
Subject: Re: [PATCH v2] net: netvsc: Update default VMBus channels

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@kernel.org/

Ignoring maintainer feedback is known to result in angry outbursts.