From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f70.google.com (mail-pa0-f70.google.com [209.85.220.70]) by kanga.kvack.org (Postfix) with ESMTP id 70BE96B0253 for ; Sun, 7 Aug 2016 22:17:50 -0400 (EDT) Received: by mail-pa0-f70.google.com with SMTP id ez1so570503612pab.1 for ; Sun, 07 Aug 2016 19:17:50 -0700 (PDT) Received: from mail-pa0-x234.google.com (mail-pa0-x234.google.com. [2607:f8b0:400e:c03::234]) by mx.google.com with ESMTPS id l5si34279945pfa.134.2016.08.07.19.17.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 07 Aug 2016 19:17:49 -0700 (PDT) Received: by mail-pa0-x234.google.com with SMTP id ti13so30522064pac.0 for ; Sun, 07 Aug 2016 19:17:49 -0700 (PDT) Date: Sun, 7 Aug 2016 19:15:27 -0700 From: Alexei Starovoitov Subject: Re: 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 Message-ID: <20160808021525.GA81429@ast-mbp> 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> <20160803174107.GA38399@ast-mbp.thefacebook.com> <20160804181913.26ee17b9@redhat.com> <1470381333.13693.48.camel@edumazet-glaptop3.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1470381333.13693.48.camel@edumazet-glaptop3.roam.corp.google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Eric Dumazet Cc: Jesper Dangaard Brouer , Brenden Blanco , davem@davemloft.net, netdev@vger.kernel.org, Jamal Hadi Salim , Saeed Mahameed , Martin KaFai Lau , Ari Saha , Or Gerlitz , john.fastabend@gmail.com, hannes@stressinduktion.org, Thomas Graf , Tom Herbert , Daniel Borkmann , Tariq Toukan , Mel Gorman , linux-mm On Fri, Aug 05, 2016 at 09:15:33AM +0200, Eric Dumazet wrote: > On Thu, 2016-08-04 at 18:19 +0200, Jesper Dangaard Brouer wrote: > > > I actually agree, that we should switch to order-0 allocations. > > > > *BUT* this will cause performance regressions on platforms with > > expensive DMA operations (as they no longer amortize the cost of > > mapping a larger page). > > > We much prefer reliable behavior, even it it is ~1 % slower than the > super-optimized thing that opens highways for attackers. +1 It's more important to have deterministic performance at fresh boot and after long uptime when high order-N are gone. > Anyway, in most cases pages are re-used, so we only call > dma_sync_single_range_for_cpu(), and there is no way to avoid this. > > Using order-0 pages [1] is actually faster, since when we use high-order > pages (multiple frames per 'page') we can not reuse the pages. > > [1] I had a local patch to allocate these pages using a very simple > allocator allocating max order (order-10) pages and splitting them into > order-0 ages, in order to lower TLB footprint. But I could not measure a > gain doing so on x86, at least on my lab machines. Which driver was that? I suspect that should indeed be the case for any driver that uses build_skb and <256 copybreak. Saeed, could you please share the performance numbers for mlx5 order-0 vs order-N ? You mentioned that there was some performance improvement. We need to know how much we'll lose when we turn off order-N. Thanks! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org