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

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Date: Thu, 14 Mar 2024 20:01:24 +0000
From: Alireza Dabagh <alid@...rosoft.com>
To: Jakub Kicinski <kuba@...nel.org>, Haiyang Zhang <haiyangz@...rosoft.com>
CC: Shradha Gupta <shradhagupta@...ux.microsoft.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>, Paul
 Rosswurm <paulros@...rosoft.com>
Subject: RE: [EXTERNAL] Re: [PATCH] net :mana : Add per-cpu stats for MANA
 device

Per processor network stats have been supported on netvsc and Mellanox NICs for years. They are also supported on Windows.

I routinely use these stats to rule in/out the issues with RSS imbalance due to either NIC not handling RSS correctly, incorrect MSI-X affinity, or not having enough entropy in flows. 

And yes, I perfectly understand that there are cases that packets received on processor x are processed (in tcp/ip stack) on processor y. But in many cases, there is a correlation between individual processor utilization and the processor where these packets are received on by the NIC.

-thanks, ali
(some suggested that I do mention on this thread that I am one of the original inventors of RSS. So there you have it. Personally I don't think that telling people "I invented the damn thing and I know what I am talking about" is the right way to handle this.) 
-----Original Message-----
From: Jakub Kicinski <kuba@...nel.org> 
Sent: Thursday, March 14, 2024 12:05 PM
To: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Shradha Gupta <shradhagupta@...ux.microsoft.com>; Shradha Gupta <shradhagupta@...rosoft.com>; linux-kernel@...r.kernel.org; linux-hyperv@...r.kernel.org; linux-rdma@...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>; Alireza Dabagh <alid@...rosoft.com>; Paul Rosswurm <paulros@...rosoft.com>
Subject: [EXTERNAL] Re: [PATCH] net :mana : Add per-cpu stats for MANA device

On Thu, 14 Mar 2024 18:54:31 +0000 Haiyang Zhang wrote:
> We understand irqbalance may be a "bad idea", and recommended some 
> customers to disable it when having problems with it... But it's still 
> enabled by default, and we cannot let all distro vendors and custom 
> image makers to disable the irqbalance. So, our host- networking team 
> is eager to have per-CPU stats for analyzing CPU usage related to 
> irqbalance or other issues.

You need a use case to get the stats upstream.
"CPU usage related to irqbalance or other issues" is both too vague, and irqbalance is a user space problem.