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Subject: Re: ix(intel) vs mlxen(mellanox) 10Gb performance
From: Daniel Braniss <danny@cs.huji.ac.il>
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Date: Tue, 18 Aug 2015 17:09:41 +0300
Cc: Rick Macklem <rmacklem@uoguelph.ca>, FreeBSD Net <freebsd-net@freebsd.org>,
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 FreeBSD stable <freebsd-stable@freebsd.org>,
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To: Hans Petter Selasky <hps@selasky.org>
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sorry, it=E2=80=99s been a tough day, we had a major meltdown, caused by =
a faulty gbic :-(
anyways, could you tell me what to do?
comment out, fix the off by one?

the machine is not yet production.

thanks,
	danny

> On 18 Aug 2015, at 16:32, Hans Petter Selasky <hps@selasky.org> wrote:
>=20
> On 08/18/15 14:53, Rick Macklem wrote:
>> 2572 	  	         ifp->if_hw_tsomax =3D 65518;
>>> >2573 	  	         ifp->if_hw_tsomaxsegcount =3D =
IXGBE_82599_SCATTER;
>>> >2574 	  	         ifp->if_hw_tsomaxsegsize =3D 2048;
>=20
> Hi,
>=20
> If IXGBE_82599_SCATTER is the maximum scatter/gather entries the =
hardware can do, remember to subtract one fragment for the TCP/IP-header =
mbuf!
>=20
> I think there is an off-by-one here:
>=20
> ifp->if_hw_tsomax =3D 65518;
> ifp->if_hw_tsomaxsegcount =3D IXGBE_82599_SCATTER - 1;
> ifp->if_hw_tsomaxsegsize =3D 2048;
>=20
> Refer to:
>=20
>>         *
>>         * NOTE: The TSO limits only apply to the data payload part of
>>         * a TCP/IP packet. That means there is no need to subtract
>>         * space for ethernet-, vlan-, IP- or TCP- headers from the
>>         * TSO limits unless the hardware driver in question requires
>>         * so.
>=20
> In sys/net/if_var.h
>=20
> Thank you!
>=20
> --HPS
>=20