From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov 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 Date: Wed, 3 Aug 2016 10:45:13 -0700 Message-ID: <20160803174107.GA38399@ast-mbp.thefacebook.com> References: <1468955817-10604-1-git-send-email-bblanco@plumgrid.com> <1468955817-10604-8-git-send-email-bblanco@plumgrid.com> <1469432120.8514.5.camel@edumazet-glaptop3.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Brenden Blanco , davem@davemloft.net, netdev@vger.kernel.org, Jamal Hadi Salim , Saeed Mahameed , Martin KaFai Lau , Jesper Dangaard Brouer , Ari Saha , Or Gerlitz , john.fastabend@gmail.com, hannes@stressinduktion.org, Thomas Graf , Tom Herbert , Daniel Borkmann , Tariq Toukan To: Eric Dumazet Return-path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:33255 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752115AbcHCRqT (ORCPT ); Wed, 3 Aug 2016 13:46:19 -0400 Received: by mail-pf0-f193.google.com with SMTP id i6so15043647pfe.0 for ; Wed, 03 Aug 2016 10:46:18 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1469432120.8514.5.camel@edumazet-glaptop3.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: 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.