From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [PATCH net-next 09/11] sfc: Prefetch RX skb header area Date: Thu, 20 Jun 2013 00:10:45 +0100 Message-ID: <1371683445.1956.134.camel@bwh-desktop.uk.level5networks.com> References: <1371680169.1956.107.camel@bwh-desktop.uk.level5networks.com> <1371680432.1956.116.camel@bwh-desktop.uk.level5networks.com> <1371681389.3252.339.camel@edumazet-glaptop> <1371681557.1956.121.camel@bwh-desktop.uk.level5networks.com> <1371682581.3252.353.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , , To: Eric Dumazet Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:16766 "EHLO webmail.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934170Ab3FSXKu (ORCPT ); Wed, 19 Jun 2013 19:10:50 -0400 In-Reply-To: <1371682581.3252.353.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2013-06-19 at 15:56 -0700, Eric Dumazet wrote: > On Wed, 2013-06-19 at 23:39 +0100, Ben Hutchings wrote: > > > You can't use build_skb() if you put multiple RX buffers in a page. See > > <1365805319.2791.18.camel@bwh-desktop.uk.solarflarecom.com>. > > Well, you use small skb (used to have 64 bytes headroom and you changed > it to 128) and attach a frag on it, so anyway build_skb() brings > nothing. > > I suspect you have a win on workloads with flood of rx, but on moderate > load sk_buff will be cold, so the cache adds latencies. > > My feeling is that this kind of tradeoff should not be per driver. Jon's testing showed a significant latency improvement. In Linux 3.10 sfc has reduced UDP performance (both latency and throughput) as we removed the support for skb pre-allocation in preparation for the implementation for DMA scatter and recycling of IOMMU-mapped buffers. The RX changes in this series are intended to recover that, and our benchmark results suggest that we succeeded. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.