[Xen-devel] Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

[Steven Rostedt <rostedt@xxxxxxxxxxx>]

On Thu, 2011-10-06 at 14:42 -0700, Jeremy Fitzhardinge wrote:
> On 10/06/2011 12:28 PM, Steven Rostedt wrote:
> >> (2) Always reserve 5 bytes of space, but if the distance is small enough
> >> patch in a 2-byte jump.  That doesn't help with the icache footprint.
> > I don't think this one is worth it.
> 
> I disagree.  This is what I benchmarked as having a 5% improvement.  If
> squashing out the padding helps, then that's a separate optimisation.

But it only speeds up the tracing case. The non-tracing case is a nop
and 5bytes is 5bytes regardless.

Did you see a 5% speed up while tracing was happening? How did you do
your test. I find a 5 byte compared to a 2 byte jump being negligible
with the rest of the overhead of tracing, but I could be wrong.

-- Steve
 


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