netdev - Re: [PATCH v2 net-next 0/8] API set for HW Buffer management

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Date:	Wed, 17 Feb 2016 23:59:58 +0100
From:	Willy Tarreau <w@....eu>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Lior Amsalem <alior@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>,
	Marcin Wojtas <mw@...ihalf.com>,
	Simon Guinot <simon.guinot@...uanux.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Timor Kardashov <timork@...vell.com>,
	Sebastian Careba <nitroshift@...oo.com>
Subject: Re: [PATCH v2 net-next 0/8] API set for HW Buffer management

Hi Gregory,

On Tue, Feb 16, 2016 at 04:33:35PM +0100, Gregory CLEMENT wrote:
> Hello,
> 
> A few weeks ago I sent a proposal for a API set for HW Buffer
> management, to have a better view of the motivation for this API see
> the cover letter of this proposal:
> http://thread.gmane.org/gmane.linux.kernel/2125152
> 
> Since this version I took into account the review from Florian:
> - The hardware buffer management helpers are no more built by default
>   and now depend on a hidden config symbol which has to be selected
>   by the driver if needed
> - The hwbm_pool_refill() and hwbm_pool_add() now receive a gfp_t as
>   argument allowing the caller to specify the flag it needs.
> - buf_num is now tested to ensure there is no wrapping
> - A spinlock has been added to protect the hwbm_pool_add() function in
>   SMP or irq context.
> 
> I also used pr_warn instead of pr_debug in case of errors.
> 
> I fixed the mvneta implementation by returning the buffer to the pool
> at various place instead of ignoring it.
> 
> About the series itself I tried to make this series easier to merge:
> - Squashed "bus: mvenus-mbus: Fix size test for
>    mvebu_mbus_get_dram_win_info" into bus: mvebu-mbus: provide api for
>    obtaining IO and DRAM window information.
> - Added my signed-otf-by on all the patches as submitter of the series.
> - Renamed the dts patches with the pattern "ARM: dts: platform:"
> - Removed the patch "ARM: mvebu: enable SRAM support in
>   mvebu_v7_defconfig" of this series and already applied it
> - Rodified the order of the patches.
> 
> In order to ease the test the branch mvneta-BM-framework-v2 is
> available at git@...hub.com:MISL-EBU-System-SW/mainline-public.git.

Well, I tested this patch series on top of latest master (from today)
on my fresh new clearfog board. I compared carefully with and without
the patchset. My workload was haproxy receiving connections and forwarding
them to my PC via the same port. I tested both with short connections
(HTTP GET of an empty file) and long ones (1 MB or more). No trouble
was detected at all, which is pretty good. I noticed a very tiny
performance drop which is more noticeable on short connections (high
packet rates), my forwarded connection rate went down from 17500/s to
17300/s. But I have not checked yet what can be tuned when using the
BM, nor did I compare CPU usage. I remember having run some tests in
the past, I guess it was on the XP-GP board, and noticed that the BM
could save a significant amount of CPU and improve cache efficiency,
so if this is the case here, we don't really care about a possible 1%
performance drop.

I'll try to provide more results as time permits.

In the mean time if you want (or plan to submit a next batch), feel
free to add a Tested-by: Willy Tarreau <w@....eu>.

cheers,
Willy