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From: David Miller <davem@davemloft.net>
Subject: Re: RFC: Removing busy-spin in pktgen.
Date: Tue, 24 Oct 2006 15:09:13 -0700 (PDT)
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From: Ben Greear <greearb@candelatech.com>
Date: Tue, 24 Oct 2006 09:34:38 -0700

> It could be a compile-time option, and even if compiled in, it should 
> only be an if  branch on
> a pointer.  Is there any noticeable performance hit for an if check if 
> you wrap it with unlikely?

It's "just an if test", yes, but it is such a test dependant
upon a memory access, and that pointer has to live somewhere
and that takes up space and conflicts with other members in
the cpu cache line.

Hooks of this nature are never free or cheap.