linux-kernel - Re: [PATCH] net :mana : Add per-cpu stats for MANA device

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Date: Wed, 13 Mar 2024 20:05:45 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Shradha Gupta <shradhagupta@...ux.microsoft.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Haiyang Zhang
 <haiyangz@...rosoft.com>, Shradha Gupta <shradhagupta@...rosoft.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Ajay Sharma
 <sharmaajay@...rosoft.com>, Leon Romanovsky <leon@...nel.org>, Thomas
 Gleixner <tglx@...utronix.de>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, KY Srinivasan <kys@...rosoft.com>, Wei Liu
 <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, Long Li
 <longli@...rosoft.com>, Michael Kelley <mikelley@...rosoft.com>
Subject: Re: [PATCH] net :mana : Add per-cpu stats for MANA device

On Wed, 13 Mar 2024 19:57:20 -0700
Shradha Gupta <shradhagupta@...ux.microsoft.com> wrote:

> Following is the data we can share:
> 
> Default interrupts affinity for each queue:
> 
>  25:          1        103          0    2989138  Hyper-V PCIe MSI 4138200989697-edge      mana_q0@pci:7870:00:00.0
>  26:          0          1    4005360          0  Hyper-V PCIe MSI 4138200989698-edge      mana_q1@pci:7870:00:00.0
>  27:          0          0          1    2997584  Hyper-V PCIe MSI 4138200989699-edge      mana_q2@pci:7870:00:00.0
>  28:    3565461          0          0          1  Hyper-V PCIe MSI 4138200989700-edge      mana_q3
> @pci:7870:00:00.0
> 
> As seen the CPU-queue mapping is not 1:1, Queue 0 and Queue 2 are both mapped 
> to cpu3. From this knowledge we can figure out the total RX stats processed by
> each CPU by adding the values of mana_q0 and mana_q2 stats for cpu3. But if
> this data changes dynamically using irqbalance or smp_affinity file edits, the
> above assumption fails. 


irqbalance is often a bad idea.
In the past, doing one shot balancing at startup was a better plan.