Re: [REGRESSION] r8169: jumbo fixes caused jumbo regressions!

On Wed, Nov 14, 2012 at 01:25:30PM +0400, Kirill Smelkov wrote:

On Tue, Nov 13, 2012 at 11:35:12PM +0100, Francois Romieu wrote:

quoted

Kirill Smelkov [off-list ref] :
[...]

quoted

My test is to stream raw video from 8 PAL cameras to net - 4 for 720x576@25 and
4 for 360x288@25 which for YUYV format occupies ~ 860 Mbps of bandwidth. The
program to transmit/receive video is here: http://repo.or.cz/w/rawv.git

[...]

quoted

quoted

(by the way, on atom system, without tx csum offload, half of cpu time
is spent only to calculate checksums...)

:o(

yes, that large. In top, my workload is

                                %sy     %id     %si
    
    default driver load         ~25     ~45     ~27
    (ethtool -k shows
     tx-checksumming: off)

    after                        ~8     ~81     ~11
    `ethtool -K eth0 tx on`
     

that's why the issue is important.

quoted

quoted

Now I wonder, where that 6K limit came from and why they say it is now
not possible to use jumbos together with tx csum offload ?

Here is an excerpt from a mail where Hayes explained the rules of
engagement back in may 2011 (John Lumby and Chris Friesen were Cced then):

Can't find that mail in gmane netdev archive and on google, to restore
full context. Was that in private?

quoted

! The Max tx sizes for 8168 series are as following:
! 
! 8168B is 4K bytes.
! 8168C and 8168CP are 6K bytes.
! 8168D and later are 9K bytes.
! 
! Note that these sizes all include head size. That is, the mtu must less than
! these values.
! You have to enable Jumbo frame feature when the tx size is large, otherwise the
! packet would not be sent. Because the hw doesn't provide the threshold, the
! checking for MTU > 1500 is just for convenience for sw.

This part is clear.

quoted

! The TSO couldn't work with some feature which need to disable hw checksum, such
! as Jumbo frame. The hw checksum have to be disabled in certain situations, so
! the TSO feature should be checked in these situations, too.

I don't enable TSO nor I need it. The text indirectly says that hw
checksum should be disabled when jumbo frames are used.

[...]

~~~~

Hayes, Realtek linux nic maintainers,

    could you please confirm that for all 8168C and 8168CP jumbo_max is
    6K and that when jumbos are used, tx checksumming should be off?

    If so, how come my two chips work stable with ~7K jumbos and tx checksum
    offload on (tested this night again for ~16 hours without any problem).

    thanks beforehand.

Dear Hayes, Realtek linux nic maintainers,

Two years ago, for current products, I've specifically choosed
motherboard with RTL8111CP, because Linux driver supported large-enough
Jumbo-frames and tx/rx offload.

Now they say that jumbo-frames should be lowered in length and tx
offload is gone, but my nics still work without problems with old ~7K
jumbos and tx checksum offload. To keep current systems working I either
have to choose another hardware, or patch the driver in contrast to what
people say was the info from the manufacturer.

Neither I like to apply risky patches nor change already proved hardware
to something else without a good reason. So please, as Realtek
representatives,

    could you please confirm that for all 8168C and 8168CP jumbo_max is
    6K and that when jumbos are used, tx checksumming should be off?


Thanks beforehand,
Kirill


P.S. If so, how come my two chips work stable with ~7K jumbos and tx
     checksum offload on (last time tested for ~16 hours without any problem)?