From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id 03E726B0005 for ; Fri, 5 Aug 2016 12:34:22 -0400 (EDT) Received: by mail-lf0-f70.google.com with SMTP id 33so156331028lfw.1 for ; Fri, 05 Aug 2016 09:34:21 -0700 (PDT) Received: from mail-wm0-x229.google.com (mail-wm0-x229.google.com. [2a00:1450:400c:c09::229]) by mx.google.com with ESMTPS id 125si7557013wmz.124.2016.08.05.00.15.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Aug 2016 00:15:37 -0700 (PDT) Received: by mail-wm0-x229.google.com with SMTP id i5so23449321wmg.0 for ; Fri, 05 Aug 2016 00:15:37 -0700 (PDT) Message-ID: <1470381333.13693.48.camel@edumazet-glaptop3.roam.corp.google.com> 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 From: Eric Dumazet Date: Fri, 05 Aug 2016 09:15:33 +0200 In-Reply-To: <20160804181913.26ee17b9@redhat.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> <20160803174107.GA38399@ast-mbp.thefacebook.com> <20160804181913.26ee17b9@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jesper Dangaard Brouer Cc: Alexei Starovoitov , 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 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. 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. -- 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