Re: [lwip-users] LWIP/WIN32 UDP performance (throughtput)

[Simon Goldschmidt]

 "Stephane Lesage" <address@hidden> wrote:

>> But then struct pbuf is still only 16 bytes long, so payload might
>> start in the middle of a 32-byte border, which leads to faults when
>> flushing cache (since the struct pbuf members are still used cached) or
>> am I wrong there?
> 
> I don't have the problem, because:
> 1. I don't need to align my payload. I just need to ensure that a cache line 
> cannot contain payload of pbuf N and struct of pbuf N+1.
> I do this by setting (PBUF_POOL_BUFSIZE + sizeof(struct pbuf)) = multiple of 
> cache line size
> 
> 2. on RX, the pbuf is owned by the driver so I can safely flush the cache to 
> get the payload, because I know the stack will not modify a value in the 
> struct.
> 

Correct me if I am wrong, but I think for this to work you have to invalidate a 
pbuf before passing it to the RX engine. When payload starts on a 32 bit 
boundary, you can leave a TX pbuf inalidated and pass it to RX.

Simon