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

From: Jakub Kicinski <kuba@kernel.org>
To: Alexander Lobakin <aleksander.lobakin@intel.com>
Cc: Jesper Dangaard Brouer <hawk@kernel.org>,
	Larysa Zaremba <larysa.zaremba@intel.com>,
	<netdev@vger.kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	<linux-kernel@vger.kernel.org>, "Christoph Hellwig" <hch@lst.de>,
	Eric Dumazet <edumazet@google.com>,
	Michal Kubiak <michal.kubiak@intel.com>,
	<intel-wired-lan@lists.osuosl.org>,
	Paolo Abeni <pabeni@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Magnus Karlsson <magnus.karlsson@intel.com>
Subject: Re: [Intel-wired-lan] [PATCH net-next 07/11] net: page_pool: add DMA-sync-for-CPU inline helpers
Date: Fri, 19 May 2023 13:45:45 -0700	[thread overview]
Message-ID: <20230519134545.5807e1d8@kernel.org> (raw)
In-Reply-To: <77d929b2-c124-d3db-1cd9-8301d1d269d3@intel.com>

On Fri, 19 May 2023 15:56:40 +0200 Alexander Lobakin wrote:
> From: Jakub Kicinski <kuba@kernel.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).