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

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Message-ID: <20240311084952.643dba6e@hermes.local>
Date: Mon, 11 Mar 2024 08:49:52 -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 Sun, 10 Mar 2024 21:19:50 -0700
Shradha Gupta <shradhagupta@...ux.microsoft.com> wrote:

> On Fri, Mar 08, 2024 at 11:22:44AM -0800, Jakub Kicinski wrote:
> > On Fri, 8 Mar 2024 18:51:58 +0000 Haiyang Zhang wrote:  
> > > > Dynamic is a bit of an exaggeration, right? On a well-configured system
> > > > each CPU should use a single queue assigned thru XPS. And for manual
> > > > debug bpftrace should serve the purpose quite well.    
> > > 
> > > Some programs, like irqbalancer can dynamically change the CPU affinity, 
> > > so we want to add the per-CPU counters for better understanding of the CPU 
> > > usage.  
> > 
> > Do you have experimental data showing this making a difference
> > in production?  
> Sure, will try to get that data for this discussion
> > 
> > Seems unlikely, but if it does work we should enable it for all
> > devices, no driver by driver.  
> You mean, if the usecase seems valid we should try to extend the framework
> mentioned by Rahul (https://lore.kernel.org/lkml/20240307072923.6cc8a2ba@kernel.org/)
> to include these stats as well?
> Will explore this a bit more and update. Thanks.
> 

Remember, statistics aren't free, and even per-cpu stats end up taking cache space.