netdev - Re: [PATCH net-next v2 0/8] net: napi: add CPU affinity to napi->config

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Message-ID: <3fc25f04-1562-4ad9-a8b4-8b85847e91fb@intel.com>
Date: Thu, 2 Jan 2025 14:38:06 -0700
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: Shay Drori <shayd@...dia.com>, <netdev@...r.kernel.org>
CC: <intel-wired-lan@...ts.osuosl.org>, <andrew+netdev@...n.ch>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<davem@...emloft.net>, <michael.chan@...adcom.com>, <tariqt@...dia.com>,
	<anthony.l.nguyen@...el.com>, <przemyslaw.kitszel@...el.com>,
	<jdamato@...tly.com>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH net-next v2 0/8] net: napi: add CPU affinity to
 napi->config



On 2024-12-22 2:23 a.m., Shay Drori wrote:
> 
> 
> On 18/12/2024 18:58, Ahmed Zaki wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> Move the IRQ affinity management to the napi struct. All drivers that are
>> already using netif_napi_set_irq() are modified to the new API. Except
>> mlx5 because it is implementing IRQ pools and moving to the new API does
>> not seem trivial.
>>
>> Tested on bnxt, ice and idpf.
>> ---
>> Opens: is cpu_online_mask the best default mask? drivers do this 
>> differently
> 
> cpu_online_mask is not the best default mask for IRQ affinity management.
> Here are two reasons:
> - Performance Gains from Driver-Specific CPU Assignment: Many drivers
>    assign different CPUs to each IRQ to optimize performance. This plays
> a crucial role in CPU utilization.
> - Impact of NUMA Node Distance on Traffic Performance: NUMA topology
>    plays a crucial role in IRQ performance. Assigning IRQs to CPUs on
>    the same NUMA node as the associated device minimizes latency caused
>    by remote memory access.[1]
> 
> [1]
> for more details on NUMA preference, you can look at commit 
> 2acda57736de1e486036b90a648e67a3599080a1
> 

Thanks for replying.

I will use cpumask_local_spread() (which now considers NUMA distances) 
in the next iteration.