Date: Sat, 4 May 2013 13:30:34 -0700 From: Richard Sharpe <realrichardsharpe@gmail.com> To: Adrian Chadd <adrian@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: Is there any way to limit the amount of data in an mbuf chain submitted to a driver? Message-ID: <CACyXjPzu3fXpo0i5YcdVBFye%2BRFTPUye=fgZ%2BycTkkiEmcRh%2BQ@mail.gmail.com> In-Reply-To: <CAJ-Vmon_5eyXMP5UOsVVBP8UgKQLw5HLMO1NgswoGb-zF=2wtg@mail.gmail.com> References: <CACyXjPwC5LRb7DT82n6PMbawceER3_nHko9c9tvrdQqceLiPww@mail.gmail.com> <CAJ-Vmon_5eyXMP5UOsVVBP8UgKQLw5HLMO1NgswoGb-zF=2wtg@mail.gmail.com>
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On Sat, May 4, 2013 at 10:39 AM, Adrian Chadd <adrian@freebsd.org> wrote: > On 4 May 2013 06:52, Richard Sharpe <realrichardsharpe@gmail.com> wrote: >> Hi folks, >> >> I understand better why I am seeing EINVAL intermittently when sending >> data from Samba via SMB2. >> >> The ixgbe driver, for TSO reasons, limits the amount of data that can >> be DMA'd to 65535 bytes. It returns EINVAL for any mbuf chain larger >> than that. >> >> The SO_SNDBUF for that socket is set to 131972. Mostly there is less >> than 64kiB of space available, so that is all TCP etc can put into the >> socket in one chain of mbufs. However, every now and then there is >> more than 65535 bytes available in the socket buffers, and we have an >> SMB packet that is larger than 65535 bytes, and we get hit. >> >> To confirm this I am going to set SO_SNDBUF back to the default of >> 65536 and test again. My repros are very reliable. >> >> However, I wondered if my only way around this if I want to continue >> to use SO_SNDBUF sizes larger than 65536 is to fragment large mbuf >> chains in the driver? > > Hm, is this is a problem without TSO? We are using the card without TSO, so I am thinking of changing that limit to 131072 and retesting. I am currently testing with SO_SNDBUF=3D32768 and have not hit the problem. > Is the problem that the NIC can't handle a frame that big, or a buffer th= at big? > Ie - if you handed the hardware two descriptors of 64k each, for the > same IP datagram, will it complain? I can't find any documentation, but it seems that with TSO it cannot handle a frame that big. Actually, since we are not using TSO, there really should not be a problem with larger frames. > Or do you need to break it up into two separate IP datagrams, facing > the driver, with a maximum size of 64k each? Not sure, but it looks like we need to do that. --=20 Regards, Richard Sharpe (=A6=F3=A5H=B8=D1=BC~=A1H=B0=DF=A6=B3=A7=F9=B1d=A1C--=B1=E4=BE=DE)
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