RE: [EXTERNAL] Re: [PATCH V2 net-next] net: mana: Assigning IRQ affinity on HT cores

[Souradeep Chakrabarti <schakrabarti@microsoft.com>]

>-----Original Message-----
>From: Jakub Kicinski <kuba@kernel.org>
>Sent: Wednesday, November 22, 2023 5:19 AM
>To: Souradeep Chakrabarti <schakrabarti@linux.microsoft.com>
>Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
><haiyangz@microsoft.com>; wei.liu@kernel.org; Dexuan Cui
><decui@microsoft.com>; davem@davemloft.net; edumazet@google.com;
>pabeni@redhat.com; Long Li <longli@microsoft.com>;
>sharmaajay@microsoft.com; leon@kernel.org; cai.huoqing@linux.dev;
>ssengar@linux.microsoft.com; vkuznets@redhat.com; tglx@linutronix.de; linux-
>hyperv@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org;
>linux-rdma@vger.kernel.org; Souradeep Chakrabarti
><schakrabarti@microsoft.com>; Paul Rosswurm <paulros@microsoft.com>
>Subject: [EXTERNAL] Re: [PATCH V2 net-next] net: mana: Assigning IRQ affinity on
>HT cores
>
>On Tue, 21 Nov 2023 05:54:37 -0800 Souradeep Chakrabarti wrote:
>> Existing MANA design assigns IRQ to every CPUs, including sibling
>> hyper-threads in a core. This causes multiple IRQs to work on same CPU
>> and may reduce the network performance with RSS.
>>
>> Improve the performance by adhering the configuration for RSS, which
>> assigns IRQ on HT cores.
>
>Drivers should not have to carry 120 LoC for something as basic as spreading IRQs.
>Please take a look at include/linux/topology.h and if there's nothing that fits your
>needs there - add it. That way other drivers can reuse it.
Because of the current design idea, it is easier to keep things inside
the mana driver code here. As the idea of IRQ distribution here is :
1)Loop through interrupts to assign CPU
2)Find non sibling online CPU from local NUMA and assign the IRQs
on them.
3)If number of IRQs is more than number of non-sibling CPU in that
NUMA node, then assign on sibling CPU of that node.
4)Keep doing it till all the online CPUs are used or no more IRQs.
5)If all CPUs in that node are used, goto next NUMA node with CPU.
Keep doing 2 and 3.
6) If all CPUs in all NUMA nodes are used, but still there are IRQs
then wrap over from first local NUMA node and continue
doing 2, 3 4 till all IRQs are assigned.