llvm dev - Sep 2013 - [LLVMdev] Enabling MI Scheduler on x86 (was Experimental Evaluation of the Schedulers in LLVM 3.3)

On Tue, Sep 24, 2013 at 1:11 AM, Andrew Trick <atrick at apple.com> wrote:
> This week, I'll see if we can enable MI scheduling by default for x86.
I'm
> not sure which flags you're using to test it now. But by making it
default
> and enabling the corresponding coalescer changes, we can be confident that
> benchmarking efforts are improving on the same baseline.

While I'm generally really excited by this, I would ask for a bit more
staging of this change.

Specifically, I would really like for a single, clear switch to enable
exactly what you want benchmark data on *before* it becomes the default,
and to give various folks time to run benchmarks and report serious
regressions.

I don't want our ability to ship LLVM from top-of-tree to be seriously
impaired by this, and enabling a feature that can have dramatic performance
impact without a giving folks a really simple way to try it out and a
period of time to run benchmarks and collect data seems to do that. =/

Once it is the default, it would be really good to leave in the single,
simple switch for a period of time for folks to disable it if need be.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130924/326463c8/attachment.html>

On Sep 23, 2013, at 11:36 PM, Chandler Carruth <chandlerc at google.com>
wrote:
> 
> On Tue, Sep 24, 2013 at 1:11 AM, Andrew Trick <atrick at apple.com>
wrote:
> This week, I'll see if we can enable MI scheduling by default for x86.
I'm not sure which flags you're using to test it now. But by making it
default and enabling the corresponding coalescer changes, we can be confident
that benchmarking efforts are improving on the same baseline.
> 
> While I'm generally really excited by this, I would ask for a bit more
staging of this change.
> 
> Specifically, I would really like for a single, clear switch to enable
exactly what you want benchmark data on *before* it becomes the default, and to
give various folks time to run benchmarks and report serious regressions.
> I don't want our ability to ship LLVM from top-of-tree to be seriously
impaired by this, and enabling a feature that can have dramatic performance
impact without a giving folks a really simple way to try it out and a period of
time to run benchmarks and collect data seems to do that. =/
> 
> Once it is the default, it would be really good to leave in the single,
simple switch for a period of time for folks to disable it if need be.

Ok. I tried to make that clear when I went through this process in July. But
I'll add another flag (in addition to the subtarget hook) to "flip the
switch" and remove the flag later.
The purpose of changing SD scheduler policy, register coalescer policy, and MI
scheduler simultaneously is only to avoid having folks who are watching
performance results waste time chasing transient regressions.

For x86, this is primarily about compile time (while continuing to avoid
worst-case scheduling). Switching the default now is to give people time to file
bugs before the next step: disabling SD scheduler.

-Andy
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130924/fd309414/attachment.html>

On Sep 23, 2013, at 11:36 PM, Chandler Carruth <chandlerc at google.com>
wrote:
> 
> On Tue, Sep 24, 2013 at 1:11 AM, Andrew Trick <atrick at apple.com>
wrote:
> This week, I'll see if we can enable MI scheduling by default for x86.
I'm not sure which flags you're using to test it now. But by making it
default and enabling the corresponding coalescer changes, we can be confident
that benchmarking efforts are improving on the same baseline.
> 
> While I'm generally really excited by this, I would ask for a bit more
staging of this change.
> 
> Specifically, I would really like for a single, clear switch to enable
exactly what you want benchmark data on *before* it becomes the default, and to
give various folks time to run benchmarks and report serious regressions.
> 
> I don't want our ability to ship LLVM from top-of-tree to be seriously
impaired by this, and enabling a feature that can have dramatic performance
impact without a giving folks a really simple way to try it out and a period of
time to run benchmarks and collect data seems to do that. =/
> 
> Once it is the default, it would be really good to leave in the single,
simple switch for a period of time for folks to disable it if need be.

I just added a flag: -misched-bench. You can use it to flip back and forth
between your target's default SD scheduler and the machine scheduler.
It's doesn't affect whether the postRA scheduler is also run.

-Andy
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130925/6dfcb500/attachment.html>

So, when the MI scheduler is enabled, will SD scheduling be totally disabled or
the SD scheduler will be automatically set to do source scheduling?

-Ghassan



________________________________
 From: Andrew Trick <atrick at apple.com>
To: llvmdev at cs.uiuc.edu 
Cc: Ghassan Shobaki <ghassan_shobaki at yahoo.com> 
Sent: Thursday, September 26, 2013 9:24 AM
Subject: Re: [LLVMdev] Enabling MI Scheduler on x86 (was Experimental Evaluation
of the Schedulers in LLVM 3.3)
 




On Sep 23, 2013, at 11:36 PM, Chandler Carruth <chandlerc at google.com>
wrote:

>
>On Tue, Sep 24, 2013 at 1:11 AM, Andrew Trick <atrick at apple.com>
wrote:
>
>This week, I'll see if we can enable MI scheduling by default for x86.
I'm not sure which flags you're using to test it now. But by making it
default and enabling the corresponding coalescer changes, we can be confident
that benchmarking efforts are improving on the same baseline.
>While I'm generally really excited by this, I would ask for a bit more
staging of this change.
>
>
>Specifically, I would really like for a single, clear switch to enable
exactly what you want benchmark data on *before* it becomes the default, and to
give various folks time to run benchmarks and report serious regressions.
>
>
>I don't want our ability to ship LLVM from top-of-tree to be seriously
impaired by this, and enabling a feature that can have dramatic performance
impact without a giving folks a really simple way to try it out and a period of
time to run benchmarks and collect data seems to do that. =/
>
>
>Once it is the default, it would be really good to leave in the single,
simple switch for a period of time for folks to disable it if need be.
I just added a flag: -misched-bench. You can use it to flip back and forth
between your target's default SD scheduler and the machine scheduler.
It's doesn't affect whether the postRA scheduler is also run.

-Andy
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130926/4337b142/attachment.html>

On Sep 25, 2013, at 11:24 PM, Andrew Trick <atrick at apple.com> wrote:
> 
> On Sep 23, 2013, at 11:36 PM, Chandler Carruth <chandlerc at
google.com> wrote:
> 
>> 
>> On Tue, Sep 24, 2013 at 1:11 AM, Andrew Trick <atrick at
apple.com> wrote:
>> This week, I'll see if we can enable MI scheduling by default for
x86. I'm not sure which flags you're using to test it now. But by making
it default and enabling the corresponding coalescer changes, we can be confident
that benchmarking efforts are improving on the same baseline.
>> 
>> While I'm generally really excited by this, I would ask for a bit
more staging of this change.
>> 
>> Specifically, I would really like for a single, clear switch to enable
exactly what you want benchmark data on *before* it becomes the default, and to
give various folks time to run benchmarks and report serious regressions.
>> 
>> I don't want our ability to ship LLVM from top-of-tree to be
seriously impaired by this, and enabling a feature that can have dramatic
performance impact without a giving folks a really simple way to try it out and
a period of time to run benchmarks and collect data seems to do that. =/
>> 
>> Once it is the default, it would be really good to leave in the single,
simple switch for a period of time for folks to disable it if need be.
> 
> 
> I just added a flag: -misched-bench. You can use it to flip back and forth
between your target's default SD scheduler and the machine scheduler.
It's doesn't affect whether the postRA scheduler is also run.
If there are still no objections, I’ll plan to switch the x86 default to MI
scheduler on Monday.

-Andy

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20131004/95cbf76a/attachment.html>