linux-kernel - Re: [Question] ixgbe：Mechanism of RSS

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Message-ID: <87b14362-cc58-496e-a38c-6db5d4025026@shopee.com>
Date: Fri, 3 Jan 2025 10:37:31 +0800
From: Haifeng Xu <haifeng.xu@...pee.com>
To: Jakub Kicinski <kuba@...nel.org>, Edward Cree <ecree.xilinx@...il.com>
Cc: 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 2025/1/3 00:39, Jakub Kicinski wrote:
> 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.

Yes, It only has 16 RSS queues.