netdev - Re: [PATCH net-next 1/2] sfc: default config to 1 channel/core in local NUMA node only

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Date:   Fri, 28 Jan 2022 14:27:28 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Íñigo Huguet <ihuguet@...hat.com>
Cc:     ecree.xilinx@...il.com, habetsm.xilinx@...il.com,
        davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] sfc: default config to 1 channel/core in
 local NUMA node only

On Fri, 28 Jan 2022 16:19:21 +0100 Íñigo Huguet wrote:
> Handling channels from CPUs in different NUMA node can penalize
> performance, so better configure only one channel per core in the same
> NUMA node than the NIC, and not per each core in the system.
> 
> Fallback to all other online cores if there are not online CPUs in local
> NUMA node.

I think we should make netif_get_num_default_rss_queues() do a similar
thing. Instead of min(8, num_online_cpus()) we should default to
num_cores / 2 (that's physical cores, not threads). From what I've seen
this appears to strike a good balance between wasting resources on
pointless queues per hyperthread, and scaling up for CPUs which have
many wimpy cores.