[lwip-users] Re: TCP tuning to increase throughput

[Mandeep Sandhu]

On Thu, Oct 1, 2009 at 7:11 PM, Mandeep Sandhu
<address@hidden> wrote:
> Hi All,
>
> I have small HTTP proxy server implemented using the lwIP sequential API.
>
> When a client connects to my webserver, the webserver proxies the
> request to another server sitting somewhere on the internet. The
> response of this server is then written back as-is to the client
> connection. All this while the client is waiting on the open socket
> connection.
>
> Roughly this is what I do:
>
> netconn_write( proxy_conn, <data to be proxied>, <length>, NETCONN_COPY);
>
>   while ((proxy_resp = netconn_recv(proxy_conn)) != NULL ) {
>       do {
>           netbuf_data(proxy_resp, &data, &len);
>           //Write response back to the client
>           err = netconn_write(client_conn, data, len, NETCONN_COPY);
>
>           if (err != ERR_OK) {
>               goto error; // some error handler
>           }
>       } while (netbuf_next(proxy_resp) >= 0);
>       netbuf_delete(proxy_resp);
>   }
>
> (this code is based on the TCP echo example)
>
> When I put debug's in the inner loop, I saw that the other end was
> sending data in chunks of 128 bytes. Even after I increase the MSS to
> 256 bytes. I was using wget on the client side, and it was reporting a
> speed of ~150 KB/s, where as a direct get of the same data from the
> server directly would be ~ 4 MB/s.
>
> Also, I saw that if the data was large (as in a large page ~200 KB), I
> was getting mem alloc error:
>
> memp_malloc: out of memory in pool TCP_PCB
>
> I've increased the pool size, but that seems to only mitigate the
> problem temporarily. Now the mem alloc error happens at slightly
> larger values (~400KB).
>
> I'm not very conversant with TCP, so any tips on how to increase
> throughput to the max and avoid the mem issue? The PBUF buffer size is
> set to 182 bytes.

An update.

I'm testing downloading a 2MB image via my proxy method explained
above. I'm getting around 1.8 Mbps throughput as shown by WGET. So for
now, I'm going to rest with this number.

Regards,
-mandeep

>
> Thanks,
> -mandeep
>