Re: Straw Poll: Restore Header Table and Static Table Indices

[Willy Tarreau <[e-mail]>]

On Tue, Oct 14, 2014 at 06:57:43PM +0000, Poul-Henning Kamp wrote:
> --------
> In message <[e-mail]>
> , Roberto Peon writes:
> 
> >So, at worst, we're talking about adding an int instead of adding a const.
> 
> It also means that the headers typically used by high-performance
> load-balancers have variable numbers, rather than fixed numbers.
> 
> That makes a BIG difference at the highest performance levels,
> in particular for hardware assist.

While in theory I agree that this is something to be considered for
*hardware* implementations, in practice the cost remains extremely
low by todays technologies. A typical 32-bit adder implemented in
45nm is 130 picoseconds [1]. Cut that in half for 16-bit. That's
with outdated technology already and not pipelined at all. In short,
it shows that a simple ASIC implemented with 2011 technology would
face a hard limit of 7-14 billion headers per second simply due to
this, so in this precise case I think that does not count, especially
if we compare this to the cost of emitting the resulting data. But
in general I tend to be very picky about microscopic costs that can
significantly limit high speed processing!

Best regards,
Willy

[1] http://www.mattkeeter.com/research/jackson.pdf