linux-kernel - Re: [Intel-wired-lan] [PATCH net-next v6 08/12] libie: add Rx buffer management (via Page Pool)

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Date:   Wed, 13 Dec 2023 12:23:43 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Amritha Nambiar <amritha.nambiar@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        <netdev@...r.kernel.org>, Alexander Duyck <alexanderduyck@...com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        "Eric Dumazet" <edumazet@...gle.com>,
        <linux-kernel@...r.kernel.org>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        <intel-wired-lan@...ts.osuosl.org>,
        David Christensen <drc@...ux.vnet.ibm.com>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH net-next v6 08/12] libie: add Rx buffer
 management (via Page Pool)

From: Jakub Kicinski <kuba@...nel.org>
Date: Mon, 11 Dec 2023 11:23:32 -0800

> On Mon, 11 Dec 2023 11:16:20 +0100 Alexander Lobakin wrote:
>> Ideally, I'd like to pass a CPU ID this queue will be run on and use
>> cpu_to_node(), but currently there's no NUMA-aware allocations in the
>> Intel drivers and Rx queues don't get the corresponding CPU ID when
>> configuring. I may revisit this later, but for now NUMA_NO_NODE is the
>> most optimal solution here.
> 
> Hm, I've been wondering about persistent IRQ mappings. Drivers
> resetting IRQ mapping on reconfiguration is a major PITA in production
> clusters. You change the RSS hash and some NICs suddenly forget
> affinitization 🤯️
> 
> The connection with memory allocations changes the math on that a bit.
> 
> The question is really whether we add CPU <> NAPI config as a netdev
> Netlink API or build around the generic IRQ affinity API. The latter 
> is definitely better from "don't duplicate uAPI" perspective.
> But we need to reset the queues and reallocate their state when 
> the mapping is changed. And shutting down queues on 
> 
>   echo $cpu > /../smp_affinity_list
> 
> seems moderately insane. Perhaps some middle-ground exists.
> 
> Anyway, if you do find cycles to tackle this - pls try to do it
> generically not just for Intel? :)

Sounds good, adding to my fathomless backlog :>

Thanks,
Olek