netdev - Re: [PATCH 00/13] mvneta Buffer Management and enhancements

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Date:	Tue, 8 Dec 2015 11:56:28 +0100
From:	Marcin Wojtas <mw@...ihalf.com>
To:	David Miller <davem@...hat.com>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	linux-kernel@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, netdev@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Yair Mahalalel <myair@...vell.com>,
	Grzegorz Jaszczyk <jaz@...ihalf.com>,
	Simon Guinot <simon.guinot@...uanux.org>,
	Evan Wang <xswang@...vell.com>, nadavh@...vell.com,
	Lior Amsalem <alior@...vell.com>,
	Tomasz Nowicki <tn@...ihalf.com>,
	Gregory Clément 
	<gregory.clement@...e-electrons.com>, nitroshift@...oo.com,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 00/13] mvneta Buffer Management and enhancements

Hi David,

2015-12-04 21:15 GMT+01:00 Florian Fainelli <f.fainelli@...il.com>:
> (no top posting please)
>
> On 02/12/15 00:26, Marcin Wojtas wrote:
>> Hi Florian,
>>
>> Can you please describe in more details, what would you expect from
>> such special abstraction layer regarding buffer managers? I'd like to
>> understand more of your expectations and evaluate possible work.
>
> Well, something along these lines:
>
> - have the ability to register a particular pool (location + number of
> buffers) in a way that is relatively device agnostic (initialization
> would of course be device specific)
>
> - provide a set of buffer management APIs like those you proposed below,
> and have some generic code that leverages what
> drivers/net/ethernet/sun/niu.c does for instance
>
> - introduce a netdev_alloc_skb_from_pool() or something like that which
> would limit the amount of code to change in your network driver to
> benefit from that feature so based
>
> I am sure David would be able to suggest more detailed API.
>

As we're getting closer to what a generic BM part, could you please
share your thoughts on the possible API?


>>>
>>>> What kind of abstraction and helpers do you mean? Some kind of API
>>>> (e.g. bm_alloc_buffer, bm_initialize_ring bm_put_buffer,
>>>> bm_get_buffer), which would be used by platform drivers (and specific
>>>> aplications if one wants to develop on top of the kernel)?
>>>>
>>>> In general, what is your top-view of such solution and its cooperation
>>>> with the drivers?
>>>
>>> The tricky parts involved have to do with allocating pages for the
>>> buffer pools and minimizing the number of atomic refcounting
>>> operations on those pages for for the puts and gets, particularly
>>> around buffer replenish runs.
>>>
>>> For example, if you're allocating a page for a buffer pool the device
>>> will chop into N (for any N < PAGE_SIZE) byte pieces, you can
>>> eliminate many atomic operations.
>

Do you think you can point to anything similar that could be a sort of
reference for such solution?

Best regards,
Marcin
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