4.1-rc1 fails with O3 optimization

4.1-rc1 fails with O3 optimization

[Andev]

Hello Newbies,

I usually compile my kernel with an unsupported O3 option(why not? :).
Today after running the latest 4.1-rc1 kernel with O3, I got a boot
failure. This is the first time this has happened for me.

If someone is interested in debugging this, please read on.

Can you try to reproduce this bug? If yes, can you also bisect this? I
am a bit swamped right now and can try to reproduce this only on
Wednesday. If you are interested, apply the following patch, compile
and see if the kernel boots. Thanks!

diff --git a/Makefile b/Makefile
index 14c722f..05950ca 100644
--- a/Makefile
+++ b/Makefile
@@ -297,8 +297,8 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then
echo $$BASH; \

 HOSTCC       = gcc
 HOSTCXX      = g++
-HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2
-fomit-frame-pointer -std=gnu89
-HOSTCXXFLAGS = -O2
+HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O3
-fomit-frame-pointer -std=gnu89
+HOSTCXXFLAGS = -O3

 ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
 HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
@@ -616,7 +616,7 @@ KBUILD_CFLAGS       += $(call
cc-option,-fno-delete-null-pointer-checks,)
 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
 KBUILD_CFLAGS  += -Os $(call cc-disable-warning,maybe-uninitialized,)
 else
-KBUILD_CFLAGS  += -O2
+KBUILD_CFLAGS  += -O3
 endif



-- 
Andev

4.1-rc1 fails with O3 optimization

[Bobby Powers]

Hello,

Andev wrote:
> I usually compile my kernel with an unsupported O3 option(why not? :).

Because there have been publications that show on major benchmarks,
the effects of -O3 are indistinguishable from noise:
http://people.cs.umass.edu/~emery/pubs/Stabilizer-UMass-CS-TR2011-43.pdf

Have you noticed that -O3 provides any performance benefits over -O2?

yours,
Bobby

4.1-rc1 fails with O3 optimization

[Andev]

On Mon, Apr 27, 2015 at 9:00 PM, Bobby Powers <bobbypowers@gmail.com> wrote:
> Hello,
>
> Andev wrote:
>> I usually compile my kernel with an unsupported O3 option(why not? :).
>
> Because there have been publications that show on major benchmarks,
> the effects of -O3 are indistinguishable from noise:
> http://people.cs.umass.edu/~emery/pubs/Stabilizer-UMass-CS-TR2011-43.pdf
>
> Have you noticed that -O3 provides any performance benefits over -O2?
>

Look here: http://www.spinics.net/lists/kernel/msg1962561.html

Btw, this will help uncover problems in either gcc or the kernel for
sure. So no harm in trying!

-- 
Andev

4.1-rc1 fails with O3 optimization

[leo kirotawa]

I could boot it using qemu. So what's the point?

On Tue, Apr 28, 2015 at 2:41 AM, Andev <debiandev@gmail.com> wrote:

> On Mon, Apr 27, 2015 at 9:00 PM, Bobby Powers <bobbypowers@gmail.com>
> wrote:
> > Hello,
> >
> > Andev wrote:
> >> I usually compile my kernel with an unsupported O3 option(why not? :).
> >
> > Because there have been publications that show on major benchmarks,
> > the effects of -O3 are indistinguishable from noise:
> > http://people.cs.umass.edu/~emery/pubs/Stabilizer-UMass-CS-TR2011-43.pdf
> >
> > Have you noticed that -O3 provides any performance benefits over -O2?
> >
>
> Look here: http://www.spinics.net/lists/kernel/msg1962561.html
>
> Btw, this will help uncover problems in either gcc or the kernel for
> sure. So no harm in trying!
>
> --
> Andev
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>



-- 

----------------------------------------------
Le?nidas S. Barbosa (Kirotawa)
blog: corecode.wordpress.com
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4.1-rc1 fails with O3 optimization

[leo kirotawa]

that .config you sent is for 4.0-rc2, is that right?


here is the diff after a make oldconfig [1]

[1] http://pastebin.com/4Lfs2it0

On Tue, Apr 28, 2015 at 12:35 PM, Andev <debiandev@gmail.com> wrote:
> On Tue, Apr 28, 2015 at 9:03 AM, leo kirotawa <kirotawa@gmail.com> wrote:
>> I could boot it using qemu. So what's the point?
>
> Could you try the attached config and see if it boots?
>
>>
>> On Tue, Apr 28, 2015 at 2:41 AM, Andev <debiandev@gmail.com> wrote:
>>>
>>> On Mon, Apr 27, 2015 at 9:00 PM, Bobby Powers <bobbypowers@gmail.com>
>>> wrote:
>>> > Hello,
>>> >
>>> > Andev wrote:
>>> >> I usually compile my kernel with an unsupported O3 option(why not? :).
>>> >
>>> > Because there have been publications that show on major benchmarks,
>>> > the effects of -O3 are indistinguishable from noise:
>>> > http://people.cs.umass.edu/~emery/pubs/Stabilizer-UMass-CS-TR2011-43.pdf
>>> >
>>> > Have you noticed that -O3 provides any performance benefits over -O2?
>>> >
>>>
>>> Look here: http://www.spinics.net/lists/kernel/msg1962561.html
>>>
>>> Btw, this will help uncover problems in either gcc or the kernel for
>>> sure. So no harm in trying!
>>>
>>> --
>>> Andev
>>>
>>> _______________________________________________
>>> Kernelnewbies mailing list
>>> Kernelnewbies at kernelnewbies.org
>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>>
>>
>>
>> --
>>
>> ----------------------------------------------
>> Le?nidas S. Barbosa (Kirotawa)
>> blog: corecode.wordpress.com
>
>
>
> --
> Andev



-- 

----------------------------------------------
Le?nidas S. Barbosa (Kirotawa)
blog: corecode.wordpress.com

4.1-rc1 fails with O3 optimization

[leo kirotawa]

With this .config you sent kernel does not boot.

On Tue, Apr 28, 2015 at 1:46 PM, leo kirotawa <kirotawa@gmail.com> wrote:
> that .config you sent is for 4.0-rc2, is that right?
>
>
> here is the diff after a make oldconfig [1]
>
> [1] http://pastebin.com/4Lfs2it0
>
> On Tue, Apr 28, 2015 at 12:35 PM, Andev <debiandev@gmail.com> wrote:
>> On Tue, Apr 28, 2015 at 9:03 AM, leo kirotawa <kirotawa@gmail.com> wrote:
>>> I could boot it using qemu. So what's the point?
>>
>> Could you try the attached config and see if it boots?
>>
>>>
>>> On Tue, Apr 28, 2015 at 2:41 AM, Andev <debiandev@gmail.com> wrote:
>>>>
>>>> On Mon, Apr 27, 2015 at 9:00 PM, Bobby Powers <bobbypowers@gmail.com>
>>>> wrote:
>>>> > Hello,
>>>> >
>>>> > Andev wrote:
>>>> >> I usually compile my kernel with an unsupported O3 option(why not? :).
>>>> >
>>>> > Because there have been publications that show on major benchmarks,
>>>> > the effects of -O3 are indistinguishable from noise:
>>>> > http://people.cs.umass.edu/~emery/pubs/Stabilizer-UMass-CS-TR2011-43.pdf
>>>> >
>>>> > Have you noticed that -O3 provides any performance benefits over -O2?
>>>> >
>>>>
>>>> Look here: http://www.spinics.net/lists/kernel/msg1962561.html
>>>>
>>>> Btw, this will help uncover problems in either gcc or the kernel for
>>>> sure. So no harm in trying!
>>>>
>>>> --
>>>> Andev
>>>>
>>>> _______________________________________________
>>>> Kernelnewbies mailing list
>>>> Kernelnewbies at kernelnewbies.org
>>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>>
>>>
>>>
>>>
>>> --
>>>
>>> ----------------------------------------------
>>> Le?nidas S. Barbosa (Kirotawa)
>>> blog: corecode.wordpress.com
>>
>>
>>
>> --
>> Andev
>
>
>
> --
>
> ----------------------------------------------
> Le?nidas S. Barbosa (Kirotawa)
> blog: corecode.wordpress.com



-- 

----------------------------------------------
Le?nidas S. Barbosa (Kirotawa)
blog: corecode.wordpress.com

4.1-rc1 fails with O3 optimization

[Andev]

On Tue, Apr 28, 2015 at 1:40 PM, leo kirotawa <kirotawa@gmail.com> wrote:
> With this .config you sent kernel does not boot.

Yup, could you try to bisect what commit is causing this failure?

-- 
Andev

4.1-rc1 fails with O3 optimization

[leo kirotawa]

Yep, I can try. Do you know when this issue start ?

On Tue, Apr 28, 2015 at 3:18 PM, Andev <debiandev@gmail.com> wrote:
> On Tue, Apr 28, 2015 at 1:40 PM, leo kirotawa <kirotawa@gmail.com> wrote:
>> With this .config you sent kernel does not boot.
>
> Yup, could you try to bisect what commit is causing this failure?
>
> --
> Andev



-- 

----------------------------------------------
Le?nidas S. Barbosa (Kirotawa)
blog: corecode.wordpress.com

4.1-rc1 fails with O3 optimization

[Andev]

On Tue, Apr 28, 2015 at 2:30 PM, leo kirotawa <kirotawa@gmail.com> wrote:
> Yep, I can try. Do you know when this issue start ?
>

I remember 4.0 working fine. You can try and use that as starting point.

-- 
Andev

4.1-rc1 fails with O3 optimization

[nick]

On 2015-04-28 03:44 PM, Andev wrote:
> On Tue, Apr 28, 2015 at 2:30 PM, leo kirotawa <kirotawa@gmail.com> wrote:
>> Yep, I can try. Do you know when this issue start ?
>>
> 
> I remember 4.0 working fine. You can try and use that as starting point.
> 
Just a question as I have been reading this for a while,is this only for x86 or other
architectures too as I would advise to bisect/test his patch on ARM and other CPU
platforms too.
Nick 

4.1-rc1 fails with O3 optimization

[Valdis.Kletnieks at vt.edu]

On Tue, 28 Apr 2015 01:41:07 -0400, Andev said:

> Look here: http://www.spinics.net/lists/kernel/msg1962561.html

I may have blinked - did you happen to mention what gcc release you are
using?
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4.1-rc1 fails with O3 optimization

[Andev]

On Tue, Apr 28, 2015 at 4:29 PM,  <Valdis.Kletnieks@vt.edu> wrote:
> On Tue, 28 Apr 2015 01:41:07 -0400, Andev said:
>
>> Look here: http://www.spinics.net/lists/kernel/msg1962561.html
>
> I may have blinked - did you happen to mention what gcc release you are
> using?

$ gcc --version
gcc-4.9.real (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2

I should indeed try with a 4.8 version too.

-- 
Andev

4.1-rc1 fails with O3 optimization

[Valdis.Kletnieks at vt.edu]

On Tue, 28 Apr 2015 17:17:37 -0400, Andev said:
> On Tue, Apr 28, 2015 at 4:29 PM,  <Valdis.Kletnieks@vt.edu> wrote:
> > On Tue, 28 Apr 2015 01:41:07 -0400, Andev said:
> >
> >> Look here: http://www.spinics.net/lists/kernel/msg1962561.html
> >
> > I may have blinked - did you happen to mention what gcc release you are
> > using?
>
> $ gcc --version
> gcc-4.9.real (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2
>
> I should indeed try with a 4.8 version too.

And 5.1.
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