netdev - Re: [PATCH v10 07/12] net/mlx4_en: add page recycle to prepare rx ring for tx support

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Message-ID: <1469432120.8514.5.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Mon, 25 Jul 2016 09:35:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Brenden Blanco <bblanco@...mgrid.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Saeed Mahameed <saeedm@....mellanox.co.il>,
	Martin KaFai Lau <kafai@...com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Ari Saha <as754m@....com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Or Gerlitz <gerlitz.or@...il.com>, john.fastabend@...il.com,
	hannes@...essinduktion.org, Thomas Graf <tgraf@...g.ch>,
	Tom Herbert <tom@...bertland.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Tariq Toukan <ttoukan.linux@...il.com>
Subject: Re: [PATCH v10 07/12] net/mlx4_en: add page recycle to prepare rx
 ring for tx support

On Tue, 2016-07-19 at 12:16 -0700, Brenden Blanco wrote:
> The mlx4 driver by default allocates order-3 pages for the ring to
> consume in multiple fragments. When the device has an xdp program, this
> behavior will prevent tx actions since the page must be re-mapped in
> TODEVICE mode, which cannot be done if the page is still shared.
> 
> Start by making the allocator configurable based on whether xdp is
> running, such that order-0 pages are always used and never shared.
> 
> Since this will stress the page allocator, add a simple page cache to
> each rx ring. Pages in the cache are left dma-mapped, and in drop-only
> stress tests the page allocator is eliminated from the perf report.
> 
> Note that setting an xdp program will now require the rings to be
> reconfigured.

Again, this has nothing to do with XDP ?

Please submit a separate patch, switching this driver to order-0
allocations.

I mentioned this order-3 vs order-0 issue earlier [1], and proposed to
send a generic patch, but had been traveling lately, and currently in
vacation.

order-3 pages are problematic when dealing with hostile traffic anyway,
so we should exclusively use order-0 pages, and page recycling like
Intel drivers.

http://lists.openwall.net/netdev/2016/04/11/88