Date: Wed, 26 Feb 2014 13:24:12 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Jack Vogel <jfvogel@gmail.com> Cc: FreeBSD Net <freebsd-net@freebsd.org>, Sami Halabi <sodynet1@gmail.com> Subject: Re: TSO Message-ID: <20140226212412.GZ92037@funkthat.com> In-Reply-To: <CAFOYbckc8=j1kAU097Y=2UjFS747O49vuWYBDLmxOqXUAOkBhw@mail.gmail.com> References: <CAEW%2BogYVto3rr6LHVsG4rOuyhXt3ZWbH2kWNk-1kAmwDKROEqg@mail.gmail.com> <20140226180736.GV92037@funkthat.com> <CAFOYbckc8=j1kAU097Y=2UjFS747O49vuWYBDLmxOqXUAOkBhw@mail.gmail.com>
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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@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."
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