Re: [lwip-users] LWIP slow web server only with Windows OS request

[Marco Giammarini]

Dear Simon,

Thanks for your reply.

I have set 40kB of heap, and every time I stop the microcontroller in debug mode during web site request, the free memory is over 70%. 

This is my configuration:

#define MEM_SIZE                (40*1024) 

#define MEMP_NUM_PBUF           28

#define MEMP_NUM_TCP_PCB        10

#define MEMP_NUM_TCP_PCB_LISTEN 3

#define MEMP_NUM_TCP_SEG        40

#define PBUF_POOL_SIZE          15

#define TCP_MSS                 (1500 - 40)

#define TCP_SND_BUF             (3*TCP_MSS) 

#define TCP_SND_QUEUELEN        (6 * TCP_SND_BUF)/TCP_MSS 

#define TCP_WND                 (3*TCP_MSS)

Is there anything I can change?

Regards,

Marco

Il giorno 15 set 2021, alle ore 09:55, goldsimon@gmx.de ha scritto:

Am 15.09.2021 um 08:55 schrieb Marco Giammarini:

Dear All, 
I’m studying this problem more in-depth (with Wireshark), and I found
that sometimes Windows reply with ACK after 40ms at every packet. In
this case, with a file of 800kB, a packet of 1460B, we have more or less
500 packets, that multiplied for 40ms reach 20 seconds each file.
I found that this problem is very common for Windows PC:
*  https://developpaper.com/lets-talk-about-the-magical-40-ms-of-tcp/
<https://developpaper.com/lets-talk-about-the-magical-40-ms-of-tcp/>
* https://docs.microsoft.com/it-it/troubleshoot/windows-server/networking/registry-entry-control-tcp-acknowledgment-behavior
<https://docs.microsoft.com/it-it/troubleshoot/windows-server/networking/registry-entry-control-tcp-acknowledgment-behavior>

Is there any way to solve the problem (or a workaround) by modify some
parameters of lwIP?

You should not have a speed problem even if the ACKs get delayed
further. Having a problem here suggests that your lwIP (memory) options
limit the send window in such amount that transmission stalls until the
next ACK is received.

Unless you're really short on memory, you should probably review your
TCP and memory related options in lwipopts.h

Regards,
Simon

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