Date: Fri, 7 Nov 2014 03:20:39 +0300 From: "Alexander V. Chernikov" <melifaro@ipfw.ru> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: svn-src-head@freebsd.org, Adrian Chadd <adrian@freebsd.org>, src-committers@freebsd.org, "Alexander V. Chernikov" <melifaro@freebsd.org>, svn-src-all@freebsd.org Subject: Re: svn commit: r273112 - head/sys/dev/ixgbe Message-ID: <67A66ECA-2550-4ABE-8405-8EC332FB84DA@ipfw.ru> In-Reply-To: <20141107001507.GD17502@onelab2.iet.unipi.it> References: <201410150122.s9F1Mudu083306@svn.freebsd.org> <545B55FA.6070408@FreeBSD.org> <20141107001507.GD17502@onelab2.iet.unipi.it>
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> On 07 Nov 2014, at 03:15, Luigi Rizzo <rizzo@iet.unipi.it> wrote: >=20 > 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 >>>=20 >>> Log: >>> Set the DROP_EN bit before the RX queue is brought up and active. >>>=20 >>> 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=20= >> and turning drop_en on) >> not only makes things a bit worse, but also makes NIC stop accounting=20= >> tail-drops as errors >> at all. >> It is a bit unhandy with HW counters, since you, for example, see 2M=20= >> packets being received >> in netstat, but in reality system receives only 1M (And there is no = easy=20 >> way to determine exact >> count). >=20 > 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 The default did change: now drop_en is turned on by default due to a = small mistake (see my comment to commit). > was ineffective. >=20 > 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. >=20 > This said, i do not understand what kind of performance degradation > you experienced, can you be more specific ? Well, I haven=E2=80=99t tested it in great details, but for my = traditional shooting (IPv4 200 dsts to single rte) I observed some = notable change, like 9.2->8.6 MPPS or similar. I=E2=80=99m not insisting that something = should be done about it, since there is no silver bullet here. My point was that we=E2=80=99ve lost an ability to count ingress errors = in stock HEAD. >=20 > cheers > luigi
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