netdev - Re: [Question] ixgbe：Mechanism of RSS

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Message-ID: <20250102083915.6e5375a1@kernel.org>
Date: Thu, 2 Jan 2025 08:39:15 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Edward Cree <ecree.xilinx@...il.com>
Cc: Haifeng Xu <haifeng.xu@...pee.com>, Eric Dumazet <edumazet@...gle.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>, Przemek Kitszel
 <przemyslaw.kitszel@...el.com>, "David S. Miller" <davem@...emloft.net>,
 Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [Question] ixgbe：Mechanism of RSS

On Thu, 2 Jan 2025 16:01:18 +0000 Edward Cree wrote:
> On 02/01/2025 11:23, Haifeng Xu wrote:
> > We want to make full use of cpu resources to receive packets. So
> > we enable 63 rx queues. But we found the rate of interrupt growth
> > on cpu 0~15 is faster than other cpus(almost twice).  
> ...
> > I am confused that why ixgbe NIC can dispatch the packets
> > to the rx queues that not specified in RSS configuration.  
> 
> Hypothesis: it isn't doing so, RX is only happening on cpus (and
>  queues) 0-15, but the other CPUs are still sending traffic and
>  thus getting TX completion interrupts from their TX queues.
> `ethtool -S` output has per-queue traffic stats which should
>  confirm this.
> 
> (But Eric is right that if you _want_ RX to use every CPU you
>  should just change the indirection table.)

IIRC Niantic had 4 bit entries in the RSS table or some such.
It wasn't possible to RSS across more than 16 queues at a time.
It's a great NIC but a bit dated at this point.