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Old 06-02-2010, 09:49 AM
Till Maas
 
Default i386-class support changed in F-13?

On Wed, Jun 02, 2010 at 08:19:24AM +0100, Peter Robinson wrote:
> On Tue, Jun 1, 2010 at 7:47 PM, Rahul Sundaram <metherid@gmail.com> wrote:
> > On 06/02/2010 12:09 PM, Peter Robinson 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.
> >>
> >
> > Can you file a ticket with FESCo? *Would be useful to track and resolve
> > this issue.
>
> I will do. I'll gather up all the bits I have an add it to the ticket.

I just created a ticket:
https://fedorahosted.org/fesco/ticket/387

Regards
Till
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Old 06-02-2010, 02:13 PM
Bruno Wolff III
 
Default i386-class support changed in F-13?

On Wed, Jun 02, 2010 at 08:19:24 +0100,
Peter Robinson <pbrobinson@gmail.com> wrote:
> On Tue, Jun 1, 2010 at 7:47 PM, Rahul Sundaram <metherid@gmail.com> wrote:
> > On 06/02/2010 12:09 PM, Peter Robinson 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.
> >>
> >
> > Can you file a ticket with FESCo? *Would be useful to track and resolve
> > this issue.
>
> I will do. I'll gather up all the bits I have an add it to the ticket.

Thanks.

This issue points out a gap in our QA testing.
Fixing it now could end up being painful (if we need to rebuild lots of
packages). Catching it earlier would have made that (lots of rebuilds)
a lot more palatible.

Also the process for changing which instructions gets used in generated
code should be looked at. The gcc people should not just be deciding this
in a vacuum. Even changing some instructions to emulation could potentially
have big performance impacts.
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Old 06-02-2010, 02:30 PM
Rahul Sundaram
 
Default i386-class support changed in F-13?

On 06/02/2010 07:43 PM, Bruno Wolff III wrote:
> This issue points out a gap in our QA testing.
> Fixing it now could end up being painful (if we need to rebuild lots of
> packages). Catching it earlier would have made that (lots of rebuilds)
> a lot more palatible.
>

Fedora 14 will have a new GCC and a mass rebuild anyway. So in this
case, we can slip in a change if needed.

Rahul
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Old 06-02-2010, 03:23 PM
David Michael
 
Default i386-class support changed in F-13?

On Wed, Jun 2, 2010 at 2:39 AM, Peter Robinson <pbrobinson@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.
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Old 06-02-2010, 03:42 PM
"Richard W.M. Jones"
 
Default i386-class support changed in F-13?

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@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.

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Old 06-02-2010, 03:56 PM
Adam Jackson
 
Default i386-class support changed in F-13?

On Tue, 2010-06-01 at 22:43 +0200, Gland Vador wrote:

> Sorry to reopen this old topic, but the conclusion is not obvious. The
> F13 is out and it seems to have lost support for the Geode LX CPU
> (cf.http://sharkcz.livejournal.com/5708.html), due to the use of the
> NOPL instruction by GCC.
>
> Will this CPU be supported during F13 and above or should I search for a
> new distribution ?

I really, really think primitive x86 support should be done as a
secondary arch.

- ajax
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Old 06-02-2010, 04:11 PM
David Michael
 
Default i386-class support changed in F-13?

Hi,

On Wed, Jun 2, 2010 at 11:42 AM, Richard W.M. Jones <rjones@redhat.com> 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

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

I wouldn't exactly use it as a gaming rig, but a silent wireless
computer on <5W power can always be used for something.
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Old 06-02-2010, 04:20 PM
"Richard W.M. Jones"
 
Default i386-class support changed in F-13?

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@redhat.com> 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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Old 06-02-2010, 09:43 PM
Adam Williamson
 
Default i386-class support changed in F-13?

On Wed, 2010-06-02 at 09:13 -0500, Bruno Wolff III wrote:

> This issue points out a gap in our QA testing.

Indeed, although there are _many_ gaps in our QA testing, and this is
not news. =) We don't have the resources to test anywhere close to
everything. The extent of claimed CPU arch support is just one of the
things we're not equipped to test...

(It does kind of surprise me that _no-one_ at OLPC managed to notice
this before release, though. We do betas!)
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Old 06-02-2010, 09:54 PM
Till Maas
 
Default i386-class support changed in F-13?

On Wed, Jun 02, 2010 at 02:43:11PM -0700, Adam Williamson wrote:
> On Wed, 2010-06-02 at 09:13 -0500, Bruno Wolff III wrote:
>
> > This issue points out a gap in our QA testing.
>
> Indeed, although there are _many_ gaps in our QA testing, and this is
> not news. =) We don't have the resources to test anywhere close to
> everything. The extent of claimed CPU arch support is just one of the
> things we're not equipped to test...
>
> (It does kind of surprise me that _no-one_ at OLPC managed to notice
> this before release, though. We do betas!)

The bug report was there one week before the announcement of the beta:
https://bugzilla.redhat.com/show_bug.cgi?id=579838

Regards
Till
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