64K NFS I/O generates a 34mbuf list for TCP which breaks TSO

[森健一]

္ငဃဂခကအဣဩဪဧေ၃၄၉၈ဏဎဍဌဋွြငအဣဤဥဦူုီိာါဧဩဪဲေံ့း်၅၅ငဃဂခက
ြဆဇဈဉညါာိီုူဪဩဧဏဎဍဌဋတထဒဓနေံ့း်၏၉ငဉဈဇဆစဋဌဍဎဏနဓဒထတပဖဗဘမ
ြ၀၁၂၉ဏဎဍဌဋတထဒဓနမဘဗဖပံံံ့း်ဲ၄၅နဓဒထတဋဌဍဎဏညဉငဃဈဂဇခဆကစအဣဤဥဦူုီ
၀မဘဝဠလရြယ၁၂၃၄၅၆၇၈၉၏၎၍၌။၊ံး်ဲဪီ္္ငဃဂခကညဉဏဈဎဇဍ၀၀၀၂၂၂၆၆၆
ေဧဩဪဲ်း့ံဿသဟှွဝဠလရြျယပဖဗဘမနဓဎဏဈဉညငဃဂခကစဆဇဈဉညါာအဣ
ဣဤဥဦူုီိာဧဩဪဲေံ့း်၏၎၍၌။၊၀၃၅၇၉ဏဉညငဃဂခကစဆဇဍဌဋဎဏနဓဒထတဪဪဩ
၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄၄
Cဟ​ဩသ္ Cဩမ္မုနိစတိဩန္ Cဩင္ရေသ္သ္.,ဤန္စ္၊စ္စ္စ္.ဒေ၊



2014-01-31 12:53 GMT+09:00 John-Mark Gurney <jmg at funkthat.com>:

> Rick Macklem wrote this message on Thu, Jan 30, 2014 at 22:32 -0500:
> > Adrian Chadd wrote:
> > > On 30 January 2014 07:06, Rick Macklem <rmacklem at uoguelph.ca> wrote:
> > > > Hi, just adding one more idea on what to do about this
> > > > to the list:
> > > > - Add a if_hw_tsomaxseg and modify the loop in tcp_output()
> > > >   so that it uses both if_hw_tsomax and if_hw_tsomaxseg to
> > > >   decide how much to hand to the device driver in each mbuf list.
> > > >   (I haven't looked to see how easy it would be to change this
> > > >   loop.)
> > >
> > > I don't think that's a hack. I think adding that and setting
> > > tsomaxseg
> > > to say 30 for now would be a good comprimise.
> > >
> > Well, my TCP is very rusty and I have no way to test it (I don't
> > have anything that does TSO), but I've attached a stab at a patch
> > to do this.
> >
> > Maybe it can be used as a starting point for this, if others think
> > it makes sense.
> >
> > The "#ifdef notyet" in the patch would become something like:
> > # if __FreeBSD_version >= NNNN
> > when a change to add if_hw_tsomaxseg is done, was what I was
> > thinking.
>
> Definately need to make sure you fix the drivers that support large
> enough sg arrays like ixgb which supports 100...
>
> Just a sampling of ones that use a _SCATTER define:
> ./e1000/if_igb.h:#define IGB_MAX_SCATTER                64
> ./e1000/if_lem.h:#define EM_MAX_SCATTER         64
> ./e1000/if_em.h:#define EM_MAX_SCATTER          32
> ./nfe/if_nfereg.h:#define       NFE_MAX_SCATTER         32
> ./ixgbe/ixgbe.h:#define IXGBE_82598_SCATTER             100
> ./ixgbe/ixgbe.h:#define IXGBE_82599_SCATTER             32
> ./ixgb/if_ixgb.h:#define IXGB_MAX_SCATTER           100
>
> I wonder how many of these are hardware limits, or just I don't
> want to allocate too much space on the stack, as 16 bytes per
> bus_dma_segment_t (on amd64) adds up...
>
> The other question is should the drivers w/ a limit on the segments
> reduce the size of the TSO packet so that we don't need to
> m_defrag/m_collapse which are expensive operations...
>
> --
>   John-Mark Gurney                              Voice: +1 415 225 5579
>
>      "All that I will do, has been done, All that I have, has not."
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