From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [RFC PATCH] dynamic_queue_limit.h: Make the struct ___cacheline_aligned_on_smp Date: Fri, 7 Dec 2012 16:42:10 +0000 Message-ID: <1354898530.2707.21.camel@bwh-desktop.uk.solarflarecom.com> References: <1354892334.29937.14.camel@joe-AO722> <1354896346.29937.43.camel@joe-AO722> <1354897144.26405.4.camel@edumazet-glaptop> <1354897761.29937.45.camel@joe-AO722> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , Tom Herbert , David Miller , netdev To: Joe Perches Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:26999 "EHLO webmail.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422760Ab2LGQmO (ORCPT ); Fri, 7 Dec 2012 11:42:14 -0500 In-Reply-To: <1354897761.29937.45.camel@joe-AO722> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2012-12-07 at 08:29 -0800, Joe Perches wrote: > On Fri, 2012-12-07 at 08:19 -0800, Eric Dumazet wrote: > > On Fri, 2012-12-07 at 08:05 -0800, Joe Perches wrote: > > > > > So it seemed somewhat sensible to make the > > > entire struct in a single cacheline. > > > > Any layout change in an object used in network fast path need a complete > > performance study. > > > > Even if you provide such a study, we'll need to reproduce your numbers > > here. > > > > BQL/DQL is not on our radars, spending two cache lines on a critical > > object is fine. > > Well Maybe Tom can provide some information as to why > the limit variable was cacheline_aligned_in_smp and not > the struct. > > I didn't find any discussion about it. Structure alignment has to be at least the maximum of each member's alignment, so the struct *is* effectively cacheline_aligned_in_smp. 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.