TSO

[John-Mark Gurney]

Jack Vogel wrote this message on Wed, Feb 26, 2014 at 10:27 -0800:
> Drivers have to work with whatever the requirements/limitations of the
> hardware,
> if you have a 5 lb sack you shouldn't be surprised if some drops when you
> shove
> 6 lbs at it :)

But right now, when that happens, the nic just drops it instead of
telling the kernel to stop giving 6 lbs sacks.. :)  It's only after a
large amount of work by various people did we even find out that this
is what was happening...

> Why not have this limit in the interface so the stack can avoid exceeding
> it?

One of the patches proposed does that, though I hope that ALL drivers
will be properly updated when the patch hits the tree...

> On Wed, Feb 26, 2014 at 10:07 AM, John-Mark Gurney <jmg at funkthat.com> wrote:
> 
> > Sami Halabi wrote this message on Wed, Feb 26, 2014 at 19:37 +0200:
> > > I'm reading (almost) all mailing emails in mailig list...
> > >
> > > Almost every / many problem in network performancr / packets loss ended
> > up
> > > suggesting disabling TSO.
> > >
> > > I wonder why.. Is it a bug in the implementation? Or bybdesign?
> > > What are the usecases that TSO is needed? Myabe  it should be disabled bt
> > > default?
> >
> > It looks like most of the problems are in drivers that don't handle
> > packets with a large number of segments properly...  The problem is
> > that some drivers limit to how segments a packet can be broken into, and
> > then if they receive such a packet, instead of doing their darnest to
> > deliver it, they drop it...
> >
> > There are some patches that help address the issue...
> >
> > Drivers should complain more loudly when a packet gets dropped by the
> > driver, since it is likely that the OS may retry the same packet,
> > just to have it fail, though sometimes it'll try a different set, and
> > it might go through, so all the user may notice is a slight lag if
> > they notice anything at all...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."