user space checksum

user space checksum

[raz ben jehuda]

I do not know if this was ever suggested.so i'll try any way.
Why not give the user the chance to supply the kernel/card with the
checksums instead of having the kernel/network card do the work ? 
This is because a user is aware to the data he sends and he can optimize
the data checksum calculations more than anyone else. for instance a web
server sends its html pages, which are static data. it can pre-calculate
the checksums.

Anyone ? 
-- 
Raz
Long Live The Penguin

Re: user space checksum

[Stephen Hemminger]

On Sun, 22 May 2005 09:51:48 +0300
raz ben jehuda <razb@bitband.com> wrote:

> I do not know if this was ever suggested.so i'll try any way.
> Why not give the user the chance to supply the kernel/card with the
> checksums instead of having the kernel/network card do the work ? 

A bad idea for two reasons:
	* application data units (APDU) do not match transport data units
	  for a stream oriented protocol. 
	* computing checksum is done for almost nothing as part
	  of the copy from user to kernel space. Modern CPU cache's
	  make computation cost << memory access cost.

> This is because a user is aware to the data he sends and he can optimize
> the data checksum calculations more than anyone else. for instance a web
> server sends its html pages, which are static data. it can pre-calculate
> the checksums.

	Tcp will compute different transfer size's based on the congestion
	window of the connection, and header part will be different.