Re: [lwip-users] Works with Win7, not Windows XP?

[ThomasJ]

Hi Niall

Not 100 correct. I receive 536 bytes segment from Win7, which doesnt crash
the lwip
WinXP sends 128 bytes segment which do crash my lwip

Thomas


Niall Donovan wrote
> With TCP_MSS = 128 and you receive 536 byte segments from XP I would
> expect
> the same number of pbufs to be used. They would simply be chained
> together.
> Is suspect your problem may not be pbufs but some other issue/ resource.
> 
> Very small pbufs may cause some isses with TCP/IP processing, for example
> lwip checks if the IP headers is fully contained in the first pbuf. IF it
> is not then it drops the packet...but shouldn't crash! Even running out of
> pbufs or heap shouldn't crash the system! lwip usually drops the packet,
> prints a warning (if enabled to do so), logs and error (if stats is on)
> and
> keeps going.
> 
> MEM_SIZE sets the Heap space used by lwip. This is only used when
> the mem_malloc() function is called. Do Grep for it in your LWIP folder
> and
> you will get an idea of what protocols call it.
> 
> If you don't already have it turned on I'd advice turning on lwip's Stats
> (LWIP_STATS = 1). If you can set break points in your code you can examine
> the global parameter 'lwip_stats' to see if any errors are logged for any
> resources or if the MAX allocation was exceeded. This includes the Heap.
> There are calls to special stats increment error functions
> (???_STATS_INC(err) ) in the code you can use  as breakpoints if your code
> crashes due to your error. Try a break point on a resource you suspect
> might be the issue and re-create the problem. If break point not
> triggered,
> it's not your problem, try another!
> 
> hope it helps.
> Niall.
> 
> 
> On 1 November 2013 09:38, ThomasJ <

> tjo@

> > wrote:
> 
>> As I read the code the each pbuf size is defined by the
>> PBUF_POOL_BUFSIZE.
>> That is defined by the TCP_MSS + 40.
>>
>> So in the case using TCP_MSS of 128 it will be 168 for each PBUF's. ??
>>
>> In the case of WinXP i will receive a lot of 128 bytes segemnts eating a
>> lot
>> of pbuf's. Then the lwip runs out and crashes?
>> In the case of Win7 I receive few 536 byte segment. Why does that not
>> take
>> as many pbuf as with winXP?
>>
>> I have increased the TCP_MSS and lowered the PBUF_POOL_SIZE and that
>> seems
>> to be good. Also for peformance. But I actually lowered the number of
>> available PBUFs for the stack.
>>
>> The define for MEM_SIZE is increased. What is the define mem size
>> actually
>> used for?
>>
>>
>>
>> Niall Donovan wrote
>> > One simple reason will be not enough pbufs allocated. Each received
>> > segment
>> > will take at lease one pbuf. Depending on the memory allocation scheme
>> you
>> > have used each pbuf might be a pre-allocated size (say 1518 + header).
>> In
>> > such a case each received segment in the win XP case will use a 1518
>> pbuf
>> > to store a 128 byte segment...it's easy to run out! For Win 7 you are
>> less
>> > likely to run out since each segment is 536 so fewer pbufs are need to
>> > save
>> > the full payload.
>> >
>> > (at lease this is my understanding of how TCP works in lwip - someone
>> > please correct me if I'm wrong!)
>> >
>> > You can have dynamic pbuf allocation - slow but possibly better use of
>> > memory.
>> > Pre-allocated fixed size pbufs pools - good performance but sizing
>> pbufs
>> > to
>> > give optimal memory use is tricky.
>> > custom pools i.e. varying size pre-allocated pbufs, picked based on
>> best
>> > fit.
>> >
>> > Which you select depends on your needs and sometimes the capability if
>> the
>> > device driver (if it uses DMA then dynamic pbuf allocation may not be
>> > possible)
>> >
>> > Niall.
>> >
>> >
>> >
>> > On 1 November 2013 07:17, ThomasJ <
>>
>> > tjo@
>>
>> > > wrote:
>> >
>> >> Hi
>> >>
>> >> I see. Thanks for reply.
>> >>
>> >> But I also wonder, why the lwip crashes when the same amount of data
>> >> comes
>> >> in segments of 128 from WindowsXP. But do not crash when the same data
>> >> comes
>> >> from Win7 in 536 bytes chunks?
>> >>
>> >> There is enough memory to receive the data (it can be received when
>> send
>> >> from Win7).
>> >>
>> >> I have changed the MSS to 536 and increased the MEM_SIZE a bit. Seems
>> to
>> >> have helped.
>> >>
>> >> Thomas
>> >>
>> >>
>> >>
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