Date: Fri, 7 Nov 2014 01:15:07 +0100 From: Luigi Rizzo <rizzo@iet.unipi.it> To: "Alexander V. Chernikov" <melifaro@freebsd.org> Cc: svn-src-head@freebsd.org, Adrian Chadd <adrian@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org Subject: Re: svn commit: r273112 - head/sys/dev/ixgbe Message-ID: <20141107001507.GD17502@onelab2.iet.unipi.it> In-Reply-To: <545B55FA.6070408@FreeBSD.org> References: <201410150122.s9F1Mudu083306@svn.freebsd.org> <545B55FA.6070408@FreeBSD.org>
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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
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