code review 12429045: runtime/pprof: test multithreaded profile, remove OS X ...

runtime/pprof: test multithreaded profile, remove OS X workarounds

This means that pprof will no longer report profiles on OS X.
That's unfortunate, but the profiles were often wrong and, worse,
it was difficult to tell whether the profile was wrong or not.

The workarounds were making the scheduler more complex,
possibly caused a deadlock (see issue 5519), and did not actually
deliver reliable results.

It may be possible for adventurous users to apply a patch to
their kernels to get working results, or perhaps having no results
will encourage someone to do the work of creating a profiling
thread like on Windows. Issue 6047 has details.

Fixes issue 5519.
Fixes issue 6047.

[rsc, 2013-08-05 20:09:56]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/

[bradfitz, 2013-08-05 20:39:24]

LGTM

I like deletions.




On Mon, Aug 5, 2013 at 1:09 PM, <rsc@golang.org> wrote:

> Reviewers: golang-dev1,
>
> Message:
> Hello golang-dev@googlegroups.com,
>
> I'd like you to review this change to
> https://code.google.com/p/go/
>
>
> Description:
> runtime/pprof: test multithreaded profile, remove OS X workarounds
>
> This means that pprof will no longer report profiles on OS X.
> That's unfortunate, but the profiles were often wrong and, worse,
> it was difficult to tell whether the profile was wrong or not.
>
> The workarounds were making the scheduler more complex,
> possibly caused a deadlock (see issue 5519), and did not actually
> deliver reliable results.
>
> It may be possible for adventurous users to apply a patch to
> their kernels to get working results, or perhaps having no results
> will encourage someone to do the work of creating a profiling
> thread like on Windows. Issue 6047 has details.
>
> Fixes issue 5519.
> Fixes issue 6047.
>
> Please review this at
https://codereview.appspot.**com/12429045/<https://codereview.appspot.com/124...
>
> Affected files:
>   M src/pkg/runtime/cpuprof.c
>   M src/pkg/runtime/lock_futex.c
>   M src/pkg/runtime/lock_sema.c
>   M src/pkg/runtime/os_darwin.c
>   M src/pkg/runtime/os_freebsd.c
>   M src/pkg/runtime/os_linux.c
>   M src/pkg/runtime/os_netbsd.c
>   M src/pkg/runtime/os_openbsd.c
>   M src/pkg/runtime/os_plan9.c
>   M src/pkg/runtime/os_windows.c
>   M src/pkg/runtime/pprof/pprof.go
>   M src/pkg/runtime/pprof/pprof_**test.go
>   M src/pkg/runtime/proc.c
>   M src/pkg/runtime/runtime.h
>   M src/pkg/runtime/signal_unix.c
>
>
> --
>
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>
>

[r, 2013-08-05 22:19:15]

I like profiles. Is there any hope of profiles coming back on OS X?

-rob

[bradfitz, 2013-08-05 22:22:47]

Issue 6047 discusses that.



On Mon, Aug 5, 2013 at 3:18 PM, Rob Pike <r@golang.org> wrote:

> I like profiles. Is there any hope of profiles coming back on OS X?
>
> -rob
>
>

[rsc, 2013-08-05 22:56:20]

On Mon, Aug 5, 2013 at 6:18 PM, Rob Pike <r@golang.org> wrote:

> I like profiles. Is there any hope of profiles coming back on OS X?
>

Yes, if only because so many of us depend on OS X. I started this because I
want to look into the json speed CLs, which means profiling, and I don't
want to pull out my Linux laptop yet again to do it.

There are two plausible ways forward.

I have accurate profiles on my OS X laptop today, for the first time ever.
I applied a tiny change to the kernel. If nothing terrible happens for the
next week or so I will post instructions for others to try.

Dmitriy has pointed out an alternative that may be more work but avoids
kernel modifications: a background thread that periodically wakes up and
samples the stacks of the other threads. This is what we do on Windows, but
it is not clear exactly how to implement it on OS X. It probably requires
talking to the Mach half of the world, as opposed to the BSD Unix half.

As Brad said, there are more details in issue 6047.

Russ

[r, 2013-08-05 22:56:23]

A tear.

-rob

[rsc, 2013-08-05 23:49:06]

*** Submitted as https://code.google.com/p/go/source/detail?r=0539958c11bb ***

runtime/pprof: test multithreaded profile, remove OS X workarounds

This means that pprof will no longer report profiles on OS X.
That's unfortunate, but the profiles were often wrong and, worse,
it was difficult to tell whether the profile was wrong or not.

The workarounds were making the scheduler more complex,
possibly caused a deadlock (see issue 5519), and did not actually
deliver reliable results.

It may be possible for adventurous users to apply a patch to
their kernels to get working results, or perhaps having no results
will encourage someone to do the work of creating a profiling
thread like on Windows. Issue 6047 has details.

Fixes issue 5519.
Fixes issue 6047.

R=golang-dev, bradfitz, r
CC=golang-dev
https://codereview.appspot.com/12429045

[dvyukov, 2013-08-06 09:14:37]

On 2013/08/05 22:56:20, rsc wrote:
> On Mon, Aug 5, 2013 at 6:18 PM, Rob Pike <mailto:r@golang.org> wrote:
> 
> > I like profiles. Is there any hope of profiles coming back on OS X?
> >
> 
> Yes, if only because so many of us depend on OS X. I started this because I
> want to look into the json speed CLs, which means profiling, and I don't
> want to pull out my Linux laptop yet again to do it.
> 
> There are two plausible ways forward.
> 
> I have accurate profiles on my OS X laptop today, for the first time ever.
> I applied a tiny change to the kernel. If nothing terrible happens for the
> next week or so I will post instructions for others to try.


Apple does not allow to view and vote for other people bugs. But the internet
says that they count how many times the same bug was submitted by different
people. People who are interested in profiling on darwin (including me) can
report this bug meaning "I am also interested in this working".