From owner-svn-src-all@FreeBSD.ORG Fri Nov 7 00:11:16 2014 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 2B5D711D; Fri, 7 Nov 2014 00:11:16 +0000 (UTC) Received: from onelab2.iet.unipi.it (onelab2.iet.unipi.it [131.114.59.238]) by mx1.freebsd.org (Postfix) with ESMTP id DF872676; Fri, 7 Nov 2014 00:11:15 +0000 (UTC) Received: by onelab2.iet.unipi.it (Postfix, from userid 275) id 913CA7300A; Fri, 7 Nov 2014 01:15:07 +0100 (CET) Date: Fri, 7 Nov 2014 01:15:07 +0100 From: Luigi Rizzo To: "Alexander V. Chernikov" Subject: Re: svn commit: r273112 - head/sys/dev/ixgbe Message-ID: <20141107001507.GD17502@onelab2.iet.unipi.it> References: <201410150122.s9F1Mudu083306@svn.freebsd.org> <545B55FA.6070408@FreeBSD.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <545B55FA.6070408@FreeBSD.org> User-Agent: Mutt/1.5.20 (2009-06-14) Cc: svn-src-head@freebsd.org, Adrian Chadd , src-committers@freebsd.org, svn-src-all@freebsd.org X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 07 Nov 2014 00:11:16 -0000 On Thu, Nov 06, 2014 at 03:05:30PM +0400, Alexander V. Chernikov wrote: > On 15.10.2014 05:22, Adrian Chadd wrote: > > Author: adrian > > Date: Wed Oct 15 01:22:56 2014 > > New Revision: 273112 > > URL: https://svnweb.freebsd.org/changeset/base/273112 > > > > Log: > > Set the DROP_EN bit before the RX queue is brought up and active. > > > > He noticed issues setting this bit in SRRCTL after the queue was up, > > so doing it from the sysctl handler isn't enough and may not actually > > work correctly. > While investigating/measuring ixgbe performance w/ and without flow control > I noticed that disabling fc entirely (e.g. disabling 512K skid buffer > and turning drop_en on) > not only makes things a bit worse, but also makes NIC stop accounting > tail-drops as errors > at all. > It is a bit unhandy with HW counters, since you, for example, see 2M > packets being received > in netstat, but in reality system receives only 1M (And there is no easy > way to determine exact > count). i'd like to point out that the default does not change (flow control is still enabled by default) and the previous handling of DROP_EN was ineffective. One may argue that FC and DROP_EN should be set independently, and i am all for it. In fact that would be the right thing to do in terms of POLA. This said, i do not understand what kind of performance degradation you experienced, can you be more specific ? cheers luigi