Date: Fri, 6 Dec 2013 12:20:12 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Michael Tuexen <Michael.Tuexen@lurchi.franken.de> Cc: Yong-Hyeon Pyun <pyunyh@gmail.com>, Jack F Vogel <jfv@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, "freebsd-net@freebsd.org list" <freebsd-net@freebsd.org> Subject: Re: A small fix for if_em.c, if_igb.c, if_ixgbe.c Message-ID: <20131206202012.GG55638@funkthat.com> In-Reply-To: <3576B69E-E943-46E0-83E5-0B2194A44ED0@lurchi.franken.de> References: <521B9C2A-EECC-4412-9F68-2235320EF324@lurchi.franken.de> <20131202022338.GA3500@michelle.cdnetworks.com> <B9593E83-E687-49E9-ABDC-B2DD615180E9@lurchi.franken.de> <20131203021658.GC2981@michelle.cdnetworks.com> <CAJ-Vmo=kfoPMYjZ0WAtqmoJMz1utXH50SW9N92RA83EMUzY7WA@mail.gmail.com> <B89B1E2D-BAF0-4815-B3AB-EB226F4F76DE@lurchi.franken.de> <CAJ-Vmo=4Zwv5V6ZYDuDLtt%2BowgbvmqyvrnrfnU%2BHeXQ3vAn-KA@mail.gmail.com> <20131205223711.GB55638@funkthat.com> <3576B69E-E943-46E0-83E5-0B2194A44ED0@lurchi.franken.de>
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Michael Tuexen wrote this message on Fri, Dec 06, 2013 at 21:17 +0100:
> On Dec 5, 2013, at 11:37 PM, John-Mark Gurney <jmg@funkthat.com> wrote:
>
> > Adrian Chadd wrote this message on Thu, Dec 05, 2013 at 14:01 -0800:
> >> On 5 December 2013 13:05, Michael Tuexen
> >> <Michael.Tuexen@lurchi.franken.de> wrote:
> >>
> >>> Just to be clear: This would mean that xxx_transmit() would return
> >>> an error even if the packet provided in the call xxx_transmit() is
> >>> enqueued and not dropped?
> >>> This would also be problem with the current SCTP stack.
> >>
> >> I think it'll return an error only if:
> >>
> >> * it queued the frame to the tail of the drbd;
> >> * it then tried to transmit a frame from the head of the drbd;
> >> * it failed to transmit the first frame in the drbd and it couldn't
> >> put it back into the queue for whatever reason.
> >>
> >> So I think it should be "ok enough" for both TCP and SCTP.
> >
> > IMO it should only return an error if the specific frame failed to be
> > sent or queued. If you cannot determine at return time if the frame
> > failed to be transmitted/queued, then it should return success.
> Yes, this is exactly what I think too. This is what my first patch
> realizes.
> >
> > In the above case, if there were other frames queued ahead, and the
> > first one failed, then it sounds like the frame may eventually be sent
> > and we will end up sending a duplicate frame.
> Correct. SCTP will consider the frame even unsent... So the SCTP stack
> behaves strange and sends a packet at wirespeed over and over again (which
> is not good...).
Sounds like a bug in SCTP, if it gets an error like that, it needs to back
off a bit.. Though when to wake up, etc, is harder to decide...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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