On Wed, Jun 02, 2010 at 12:11:26PM -0400, David Michael wrote:
> Hi,
>
> On Wed, Jun 2, 2010 at 11:42 AM, Richard W.M. Jones <rjones@xxxxxxxxxx> wrote:
> > I wonder what the performance impact is. NOPL appears to be a
> > variable length NOP (no-op). Obviously a very useful instruction for
> > things like alignment, and gcc seems to stuff lots of them into the
> > code:
> >
> > $ objdump -d /bin/ls | wc -l
> > 16867
> > $ objdump -d /bin/ls | grep nopl | wc -l
> > 369
> >
> > 369/16867 ~ 2%
> >
> > This is not a very fair comparison because we'd want to know how
> > frequently NOPL is executed, but I hope it shows that these
> > instructions are not infrequent.
>
> I recall checking this when F12 was declared to go i686 but retain
> support for Geode LX CPUs. NOPLs were common in x86_64, but seemed to
> be very infrequent in 32-bit land (which is what would run on a Geode
> anyway).
>
> To see if this is still the case, I downloaded and extracted F13's
> 32-bit coreutils, and no binary appears to contain a single NOPL.
> (Though I get a similar result as your test with x86_64.)
>
> objdump -d {,usr/}{,s}bin/* | grep -Fc nopl
> 0
Ah very true. I was forgetting that they were 32 bit.
(I even *have* one of them :-)
Rich.
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