Is there any way to limit the amount of data in an mbuf chain submitted to a driver?

[Richard Sharpe]

On Sat, May 4, 2013 at 2:18 PM, Jack Vogel <jfvogel at gmail.com> wrote:
> Ahh, Twinville, new hardware :)  The version at the tip is 2.5.8 and I am
> working on version 2.5.12 internally that I hope to commit next week...
> so your version is "a bit old" :) I would do some testing on newer code.

I would love to. Where is the repo.

> Jack
>
>
>
> On Sat, May 4, 2013 at 1:54 PM, Richard Sharpe <realrichardsharpe at gmail.com>
> wrote:
>>
>> On Sat, May 4, 2013 at 1:41 PM, Jack Vogel <jfvogel at gmail.com> wrote:
>> > If you don't use TSO you will hurt your TX performance significantly
>> > from
>> > the tests that I've run. What exactly is the device you are using, I
>> > don't
>> > have the source in front of me now, but I'm almost sure that the limit
>> > is
>> > not 64K but 256K, or are you using some ancient version of the driver?
>>
>>             ix0 pnpinfo vendor=0x8086 device=0x1528 subvendor=0x8086
>> subdevice=0x0001 class=0x020000 at slot=0 function=0
>>             ix1 pnpinfo vendor=0x8086 device=0x1528 subvendor=0x8086
>> subdevice=0x0001 class=0x020000 at slot=0 function=1
>>
>> The version calls itself ixgbe-2.4.4 ...
>>
>> Hmmm, copyright is 2001-2010 ... so perhaps a bit old.
>>
>> > Jack
>> >
>> >
>> >
>> > On Sat, May 4, 2013 at 1:30 PM, Richard Sharpe
>> > <realrichardsharpe at gmail.com>
>> > wrote:
>> >>
>> >> On Sat, May 4, 2013 at 10:39 AM, Adrian Chadd <adrian at freebsd.org>
>> >> wrote:
>> >> > On 4 May 2013 06:52, Richard Sharpe <realrichardsharpe at 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=32768 and have not hit the
>> >> problem.
>> >>
>> >> > Is the problem that the NIC can't handle a frame that big, or a
>> >> > buffer
>> >> > that 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.
>> >>
>> >>
>> >> --
>> >> Regards,
>> >> Richard Sharpe
>> >> (何以解憂？唯有杜康。--曹操)
>> >> _______________________________________________
>> >> freebsd-net at freebsd.org mailing list
>> >> http://lists.freebsd.org/mailman/listinfo/freebsd-net
>> >> To unsubscribe, send any mail to "freebsd-net-unsubscribe at freebsd.org"
>> >
>> >
>>
>>
>>
>> --
>> Regards,
>> Richard Sharpe
>> (何以解憂？唯有杜康。--曹操)
>
>



-- 
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)