i386-class support changed in F-13?

[Richard W.M. Jones]

On Wed, Jun 02, 2010 at 11:23:37AM -0400, David Michael wrote:
> On Wed, Jun 2, 2010 at 2:39 AM, Peter Robinson <pbrobinson at gmail.com> wrote:
> > It does work in F-12, the response for the lack of support in F-13 was
> > 'deal with it'. There is suppose to be a patch to emulate it in the
> > kernel but apparently it won't go upstream until its a generic infra
> > patch that can allow support of other emulated bits in other cpus in a
> > generic way. So its possible it will come back, but I don't hold up
> > hope of a quick resolution. Which leaves us in a big predicament as to
> > how we're going to support the 1.5 million odd XO-1s out there moving
> > forward.
> 
>   I believe this was the latest post of the NOPL emulation patch:
> http://lkml.org/lkml/2010/3/1/430  This is not the general instruction
> emulator mentioned, but a fix intended just for getting the Geode LX
> classed as i686.
> 
>   I haven't used this patch myself yet; my Geode LX machine runs an
> older Fedora, so it still works.  I suppose I'll need to try the patch
> during the next upgrade until things are settled.

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.

Having said that, AMD Geodes are slowwwwww anyway ...

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://et.redhat.com/~rjones/virt-df/