linux-kernel - Re: [PATCH net-next 06/16] idpf: a use saner limit for default number of queues to allocate

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Message-ID: <ae42f7a3-10dd-4b5a-8bd0-fbab0148a419@intel.com>
Date: Wed, 12 Mar 2025 18:22:06 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
CC: <intel-wired-lan@...ts.osuosl.org>, Michal Kubiak
	<michal.kubiak@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>, "Przemek
 Kitszel" <przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Alexei
 Starovoitov" <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
	"Jesper Dangaard Brouer" <hawk@...nel.org>, John Fastabend
	<john.fastabend@...il.com>, Simon Horman <horms@...nel.org>,
	<bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 06/16] idpf: a use saner limit for default number
 of queues to allocate

From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Date: Fri, 7 Mar 2025 11:32:15 +0100

> On Wed, Mar 05, 2025 at 05:21:22PM +0100, Alexander Lobakin wrote:
>> Currently, the maximum number of queues available for one vport is 16.
>> This is hardcoded, but then the function calculating the optimal number
>> of queues takes min(16, num_online_cpus()).
>> On order to be able to allocate more queues, which will be then used for
> 
> nit: s/On/In

Also "use a saner limit", not "a use saner limit" in the subject =\

> 
>> XDP, stop hardcoding 16 and rely on what the device gives us. Instead of
>> num_online_cpus(), which is considered suboptimal since at least 2013,
>> use netif_get_num_default_rss_queues() to still have free queues in the
>> pool.
> 
> Should we update older drivers as well?

That would be good.

For idpf, this is particularly important since the current logic eats
128 Tx queues for skb traffic on my Xeon out of 256 available by default
(per vport). On a 256-thread system, it would eat the whole limit,
leaving nothing for XDP >_< ice doesn't have a per-port limit IIRC.

> 
>> nr_cpu_ids number of Tx queues are needed only for lockless XDP sending,
>> the regular stack doesn't benefit from that anyhow.
>> On a 128-thread Xeon, this now gives me 32 regular Tx queues and leaves
>> 224 free for XDP (128 of which will handle XDP_TX, .ndo_xdp_xmit(), and
>> XSk xmit when enabled).

Thanks,
Olek