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Date:      Tue, 18 Aug 2015 17:09:41 +0300
From:      Daniel Braniss <danny@cs.huji.ac.il>
To:        Hans Petter Selasky <hps@selasky.org>
Cc:        Rick Macklem <rmacklem@uoguelph.ca>, FreeBSD Net <freebsd-net@freebsd.org>, Slawa Olhovchenkov <slw@zxy.spb.ru>, FreeBSD stable <freebsd-stable@freebsd.org>, Christopher Forgeron <csforgeron@gmail.com>
Subject:   Re: ix(intel) vs mlxen(mellanox) 10Gb performance
Message-ID:  <47EC9292-082C-4801-B52F-4BD6B8310F99@cs.huji.ac.il>
In-Reply-To: <55D333D6.5040102@selasky.org>
References:  <1D52028A-B39F-4F9B-BD38-CB1D73BF5D56@cs.huji.ac.il> <20150817094145.GB3158@zxy.spb.ru> <CAB2_NwBOLcL4EVjFN6=BvBC_YN=gmfZMweVbmb5ZPCsK4Hnx1g@mail.gmail.com> <17871443-E105-4434-80B1-6939306A865F@cs.huji.ac.il> <473274181.23263108.1439814072514.JavaMail.zimbra@uoguelph.ca> <7F892C70-9C04-4468-9514-EDBFE75CF2C6@cs.huji.ac.il> <805850043.24018217.1439848150695.JavaMail.zimbra@uoguelph.ca> <9D8B0503-E8FA-43CA-88F0-01F184F84D9B@cs.huji.ac.il> <1721122651.24481798.1439902381663.JavaMail.zimbra@uoguelph.ca> <55D333D6.5040102@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




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