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

[ThomasJ]

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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