netdev - Re: [Intel-wired-lan] [PATCH net-next 07/11] net: page_pool: add DMA-sync-for-CPU inline helpers

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Message-ID: <20230519134545.5807e1d8@kernel.org>
Date: Fri, 19 May 2023 13:45:45 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>, Larysa Zaremba
 <larysa.zaremba@...el.com>, <netdev@...r.kernel.org>, Ilias Apalodimas
 <ilias.apalodimas@...aro.org>, <linux-kernel@...r.kernel.org>, "Christoph
 Hellwig" <hch@....de>, Eric Dumazet <edumazet@...gle.com>, Michal Kubiak
 <michal.kubiak@...el.com>, <intel-wired-lan@...ts.osuosl.org>, Paolo Abeni
 <pabeni@...hat.com>, "David S. Miller" <davem@...emloft.net>, Magnus
 Karlsson <magnus.karlsson@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH net-next 07/11] net: page_pool: add
 DMA-sync-for-CPU inline helpers

On Fri, 19 May 2023 15:56:40 +0200 Alexander Lobakin wrote:
> From: Jakub Kicinski <kuba@...nel.org>
> Date: Thu, 18 May 2023 13:36:27 -0700
> >> I'll definitely take a look, I also like the idea of minimalistic and
> >> lightweight headers.
> >> page_pool.h and page_pool_drv.h? :D  
> > 
> > What I've been doing lately is split like this:
> > 
> > include/net/something.h           (simply includes all other headers)
> > include/net/something/types.h     (structs, defines, enums)
> > include/net/something/functions.h (inlines and function declarations)
> > 
> > If that's reasonable -- we should put the helpers under
> > 
> > include/net/page_pool/functions.h ?  
> 
> Hmm, all files that need something from page_pool.h usually need both
> types and functions. Not sure we'll benefit anything here.

Ack, in the scheme above most places (source files) would include
something.h, the something/types.h is just for other headers.
something/functions.h is basically never included directly.

> OTOH leaving
> those sync-for-cpu inlines alone allows to avoid including dma-mapping.h
> and currently only IAVF needs them. So my idea is:
> 
> - you need smth from PP, but not sync-for-cpu -- more lightweight
>   page_pool.h is for you;
> - you need sync-for-cpu (or maybe something else with heavy deps in the
>   future) -- just include page_pool_drv.h.

The idea makes sense in isolation, but I'm trying to figure out
a convention which would not require case-by-case discussions.

> I tried moving something else, but couldn't find anything that would
> give any win. <linux/mm.h> and <linux/ptr_ring.h> are needed to define
> `struct page_pool`, i.e. even being structured like in your example they
> would've gone into pp/types.h =\
> `struct ptr_ring` itself doesn't require any MM-related definitions, so
> would we split it into ptr_ring/{types,functions}.h, we could probably
> avoid a couple includes :D

Ack, not saying that we need to split now, it's just about the naming
(everyone's favorite topic).

I think that it's a touch weird to name the header _drv.h and then
include it in the core in multiple places (*cough* xdp_sock_drv.h). 
Also If someone needs to add another "heavy" static line for use by 
the core they will try to put it in page_pool.h rather than _drv.h...

I'd rather split the includes by the basic language-level contents,
first, then by the intended consumer, only if necessary. Language 
level sorting require less thinking :)

But none of this is important, if you don't wanna to do it, just keep 
the new helpers in page_pool.h (let's not do another _drv.h).