Date: Mon, 4 Feb 2013 13:28:35 -0500 From: Randy Stewart <randall@lakerest.net> To: Jack Vogel <jfvogel@gmail.com> Cc: Kip Macy <kmacy@freebsd.org>, John Baldwin <jhb@freebsd.org>, freebsd-net <freebsd-net@freebsd.org>, Robert Watson <rwatson@freebsd.org>, Jack F Vogel <jfv@freebsd.org> Subject: Re: Driver patch to look at... Message-ID: <FBC11DFB-BEC7-4025-8F2D-9E2E03CAA0A7@lakerest.net> In-Reply-To: <CAFOYbcmZU%2B1Ks9962wcEqTVvg5juWYLfePZw8Y0xm%2BKbAvN3qw@mail.gmail.com> References: <D3AA078A-CD19-4228-A019-BE9C985895E2@lakerest.net> <CAFOYbcmZU%2B1Ks9962wcEqTVvg5juWYLfePZw8Y0xm%2BKbAvN3qw@mail.gmail.com>
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I am beating the heck out of it on my 9.x testbed where I lifted it = from. I don't have any ix or ixgbe cards to play with yet though.. R On Feb 4, 2013, at 1:11 PM, Jack Vogel wrote: >=20 >=20 > On Mon, Feb 4, 2013 at 9:22 AM, Randy Stewart <randall@lakerest.net> = wrote: > All: >=20 > I have been working with TCP in gigabit networks (igb driver actually) = and have > found a very nasty problem with the way the driver is doing its put = back when > it fills the out-bound transmit queue. >=20 > Basically it has taken a packet from the head of the ring buffer, and = then > realizes it can't fit it into the transmit queue. So it just = re-enqueue's it > into the ring buffer. Whats wrong with that? Well most of the time = there > are anywhere from 10-50 packets (maybe more) in that ring buffer when = you are > operating at full speed (or trying to). This means you will see 10 = duplicate > ACKs, do a fast retransmit and cut your cwnd in half.. not very nice = actually. >=20 > The patch I have attached makes it so that >=20 > 1) There are ways to swap back. > 2) Use the peek in the ring buffer and only > dequeue the packet if we put it into the transmit ring > 3) If something goes wrong and the transmit frees the packet we = dequeue it. > 4) If the transmit changed it (defrag etc) then swap out the new mbuf = that > has taken its place. >=20 > I have fixed the four intel drivers that had this systemic issue, but = there > are still more to fix. >=20 > Comments/review .. rotten egg's etc.. would be most welcome before > I commit this.. >=20 > Jack are you out there? >=20 >=20 > Yes, I'm usually perceived as being 'out there' :) If you had = addressed it to 'jfv' rather than 'jv' it would have worked better. >=20 > I have no theoretical objection to this, how much testing has it had? >=20 > Jack >=20 ----- Randall Stewart randall@lakerest.net
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