netdev - Re: [PATCH net-next v2 4/8] net: napi: add CPU affinity to napi->config

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Message-ID: <20241220092356.69c9aa1e@kernel.org>
Date: Fri, 20 Dec 2024 09:23:56 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Ahmed Zaki <ahmed.zaki@...el.com>
Cc: <netdev@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>,
 <andrew+netdev@...n.ch>, <edumazet@...gle.com>, <pabeni@...hat.com>,
 <davem@...emloft.net>, <michael.chan@...adcom.com>, <tariqt@...dia.com>,
 <anthony.l.nguyen@...el.com>, <przemyslaw.kitszel@...el.com>,
 <jdamato@...tly.com>, <shayd@...dia.com>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH net-next v2 4/8] net: napi: add CPU affinity to
 napi->config

On Fri, 20 Dec 2024 07:51:09 -0700 Ahmed Zaki wrote:
> On 2024-12-19 8:42 p.m., Jakub Kicinski wrote:
> > On Wed, 18 Dec 2024 09:58:39 -0700 Ahmed Zaki wrote:  
> >> +	if (!glue_created && flags & NAPIF_IRQ_AFFINITY) {
> >> +		glue = kzalloc(sizeof(*glue), GFP_KERNEL);
> >> +		if (!glue)
> >> +			return;
> >> +		glue->notify.notify = netif_irq_cpu_rmap_notify;
> >> +		glue->notify.release = netif_napi_affinity_release;
> >> +		glue->data = napi;
> >> +		glue->rmap = NULL;
> >> +		napi->irq_flags |= NAPIF_IRQ_NORMAP;  
> > 
> > Why allocate the glue? is it not possible to add the fields:
> > 
> > 	struct irq_affinity_notify notify;
> > 	u16 index;
> > 
> > to struct napi_struct ?  
> 
> In the first branch of "if", the cb function netif_irq_cpu_rmap_notify() 
> is also passed to irq_cpu_rmap_add() where the irq notifier is embedded 
> in "struct irq_glue".

I don't understand what you're trying to say, could you rephrase?

> I think this cannot be changed as long as some drivers are directly 
> calling irq_cpu_rmap_add() instead of the proposed API.

Drivers which are not converted shouldn't matter if we have our own
notifier and call cpu_rmap_update() directly, no?

Drivers which are converted should not call irq_cpu_rmap_add().