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Message-ID: <20160803174107.GA38399@ast-mbp.thefacebook.com> Date: Wed, 3 Aug 2016 10:45:13 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Brenden Blanco <bblanco@...mgrid.com>, 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>, 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: order-0 vs order-N driver allocation. Was: [PATCH v10 07/12] net/mlx4_en: add page recycle to prepare rx ring for tx support On Mon, Jul 25, 2016 at 09:35:20AM +0200, Eric Dumazet wrote: > 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 Completely agree. These multi-page tricks work only for benchmarks and not for production. Eric, if you can submit that patch for mlx4 that would be awesome. I think we should default to order-0 for both mlx4 and mlx5. Alternatively we're thinking to do a netlink or ethtool switch to preserve old behavior, but frankly I don't see who needs this order-N allocation schemes.
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