llvm dev - Dec 2018 - [RFC] Moving tools/llvm-mca/lib into lib/MCA

(on the correct mailing list)


Hi all,

tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
create a new MCA library in LLVM.

llvm-mca has recently been split
<https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and the
tool part.

   -

   The core part simulates the execution of a basic block of machine
   instructions as modeled by the llvm SchedModel.
   -

   The tool part deals with the plumbing and interacting with the user.


The core part can be used by parts of LLVM that deal with cost modeling
(e.g. scheduling and vectorization). MCA provides a more realistic target
for optimization than the heuristics typically used to drive these passes.
We think that using approaches based on fine-grained cost modeling can
greatly improve the performance of critically hot code, by trading compile
time for performance.

As an example of how MCA can be used to improve scheduling, we have built a
prototype machine scheduler that optimizes the simulated latency of a block
of code under the constraints of the scheduling DAG. We've had interesting
wins of 2-3% on assembly kernels for webp
<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.

The patch is completely mechanical and can be seen here
<https://reviews.llvm.org/D55557>. It only moves the files and updates all
references.

We'd like to hear if there are any things comments/objections to this
change.

Thanks !

*note: We did this before llvm-mca was released and were using a different
simulator, but the idea remains the same.

On Wed, Dec 12, 2018 at 11:44 AM Clement Courbet <courbet at google.com>
wrote:
> Hi all,
>
> tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
> create a new MCA library in LLVM.
>
> llvm-mca has recently been split
> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and
the
> tool part.
>
>    -
>
>    The core part simulates the execution of a basic block of machine
>    instructions as modeled by the llvm SchedModel.
>    -
>
>    The tool part deals with the plumbing and interacting with the user.
>
>
> The core part can be used by parts of LLVM that deal with cost modeling
> (e.g. scheduling and vectorization). MCA provides a more realistic target
> for optimization than the heuristics typically used to drive these passes.
> We think that using approaches based on fine-grained cost modeling can
> greatly improve the performance of critically hot code, by trading compile
> time for performance.
>
> As an example of how MCA can be used to improve scheduling, we have built
> a prototype machine scheduler that optimizes the simulated latency of a
> block of code under the constraints of the scheduling DAG. We've had
> interesting wins of 2-3% on assembly kernels for webp
>
<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>
> The patch is completely mechanical and can be seen here
> <https://reviews.llvm.org/D55557>. It only moves the files and
updates
> all references.
>
> We'd like to hear if there are any things comments/objections to this
> change.
>
> Thanks !
>
> *note: We did this before llvm-mca was released and were using a different
> simulator, but the idea remains the same.
>
>
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Thanks Clement for working on this.

I like the idea of moving the core abstractions of llvm-mca in llvm/lib, as
it potentially enables a number of interesting use cases and future
developments.

As you wrote, the patch is very simple (a pretty mechanical
change).
>From my point of view, this all looks good. Let see if other people have
the same opinion on this.

-Andrea


On Wed, Dec 12, 2018 at 11:58 AM Clement Courbet <courbet at google.com>
wrote:
> (on the correct mailing list)
>
>
> Hi all,
>
> tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
> create a new MCA library in LLVM.
>
> llvm-mca has recently been split
> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and
the
> tool part.
>
>    -
>
>    The core part simulates the execution of a basic block of machine
>    instructions as modeled by the llvm SchedModel.
>    -
>
>    The tool part deals with the plumbing and interacting with the user.
>
>
> The core part can be used by parts of LLVM that deal with cost modeling
> (e.g. scheduling and vectorization). MCA provides a more realistic target
> for optimization than the heuristics typically used to drive these passes.
> We think that using approaches based on fine-grained cost modeling can
> greatly improve the performance of critically hot code, by trading compile
> time for performance.
>
> As an example of how MCA can be used to improve scheduling, we have built
> a prototype machine scheduler that optimizes the simulated latency of a
> block of code under the constraints of the scheduling DAG. We've had
> interesting wins of 2-3% on assembly kernels for webp
>
<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>
> The patch is completely mechanical and can be seen here
> <https://reviews.llvm.org/D55557>. It only moves the files and
updates
> all references.
>
> We'd like to hear if there are any things comments/objections to this
> change.
>
> Thanks !
>
> *note: We did this before llvm-mca was released and were using a different
> simulator, but the idea remains the same.
>
> On Wed, Dec 12, 2018 at 11:44 AM Clement Courbet <courbet at
google.com>
> wrote:
>
>> Hi all,
>>
>> tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA
and
>> create a new MCA library in LLVM.
>>
>> llvm-mca has recently been split
>> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part
and the
>> tool part.
>>
>>    -
>>
>>    The core part simulates the execution of a basic block of machine
>>    instructions as modeled by the llvm SchedModel.
>>    -
>>
>>    The tool part deals with the plumbing and interacting with the user.
>>
>>
>> The core part can be used by parts of LLVM that deal with cost modeling
>> (e.g. scheduling and vectorization). MCA provides a more realistic
target
>> for optimization than the heuristics typically used to drive these
passes.
>> We think that using approaches based on fine-grained cost modeling can
>> greatly improve the performance of critically hot code, by trading
compile
>> time for performance.
>>
>> As an example of how MCA can be used to improve scheduling, we have
built
>> a prototype machine scheduler that optimizes the simulated latency of a
>> block of code under the constraints of the scheduling DAG. We've
had
>> interesting wins of 2-3% on assembly kernels for webp
>>
<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
>> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>>
>> The patch is completely mechanical and can be seen here
>> <https://reviews.llvm.org/D55557>. It only moves the files and
updates
>> all references.
>>
>> We'd like to hear if there are any things comments/objections to
this
>> change.
>>
>> Thanks !
>>
>> *note: We did this before llvm-mca was released and were using a
>> different simulator, but the idea remains the same.
>>
>>
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Makes sense to me.  Should CODE_OWNERS.TXT also be updated to reflect the
move too?

On Wed, 12 Dec 2018 at 12:52, Andrea Di Biagio <andrea.dibiagio at
gmail.com>
wrote:
> Thanks Clement for working on this.
>
> I like the idea of moving the core abstractions of llvm-mca in llvm/lib,
> as it potentially enables a number of interesting use cases and future
> developments.
>
> As you wrote, the patch is very simple (a pretty mechanical change).
> From my point of view, this all looks good. Let see if other people have
> the same opinion on this.
>
> -Andrea
>
>
> On Wed, Dec 12, 2018 at 11:58 AM Clement Courbet <courbet at
google.com>
> wrote:
>
>> (on the correct mailing list)
>>
>>
>> Hi all,
>>
>> tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA
and
>> create a new MCA library in LLVM.
>>
>> llvm-mca has recently been split
>> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part
and the
>> tool part.
>>
>>    -
>>
>>    The core part simulates the execution of a basic block of machine
>>    instructions as modeled by the llvm SchedModel.
>>    -
>>
>>    The tool part deals with the plumbing and interacting with the user.
>>
>>
>> The core part can be used by parts of LLVM that deal with cost modeling
>> (e.g. scheduling and vectorization). MCA provides a more realistic
target
>> for optimization than the heuristics typically used to drive these
passes.
>> We think that using approaches based on fine-grained cost modeling can
>> greatly improve the performance of critically hot code, by trading
compile
>> time for performance.
>>
>> As an example of how MCA can be used to improve scheduling, we have
built
>> a prototype machine scheduler that optimizes the simulated latency of a
>> block of code under the constraints of the scheduling DAG. We've
had
>> interesting wins of 2-3% on assembly kernels for webp
>>
<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
>> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>>
>> The patch is completely mechanical and can be seen here
>> <https://reviews.llvm.org/D55557>. It only moves the files and
updates
>> all references.
>>
>> We'd like to hear if there are any things comments/objections to
this
>> change.
>>
>> Thanks !
>>
>> *note: We did this before llvm-mca was released and were using a
>> different simulator, but the idea remains the same.
>>
>> On Wed, Dec 12, 2018 at 11:44 AM Clement Courbet <courbet at
google.com>
>> wrote:
>>
>>> Hi all,
>>>
>>> tl;dr: We'd like to propose moving tools/llvm-mca/lib into
lib/MCA and
>>> create a new MCA library in LLVM.
>>>
>>> llvm-mca has recently been split
>>> <https://bugs.llvm.org/show_bug.cgi?id=37696> into its core
part and
>>> the tool part.
>>>
>>>    -
>>>
>>>    The core part simulates the execution of a basic block of
machine
>>>    instructions as modeled by the llvm SchedModel.
>>>    -
>>>
>>>    The tool part deals with the plumbing and interacting with the
user.
>>>
>>>
>>> The core part can be used by parts of LLVM that deal with cost
modeling
>>> (e.g. scheduling and vectorization). MCA provides a more realistic
target
>>> for optimization than the heuristics typically used to drive these
passes.
>>> We think that using approaches based on fine-grained cost modeling
can
>>> greatly improve the performance of critically hot code, by trading
compile
>>> time for performance.
>>>
>>> As an example of how MCA can be used to improve scheduling, we have
>>> built a prototype machine scheduler that optimizes the simulated
latency of
>>> a block of code under the constraints of the scheduling DAG.
We've had
>>> interesting wins of 2-3% on assembly kernels for webp
>>>
<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
>>> and gemmlowp <https://github.com/google/gemmlowp/pull/91>*.
>>>
>>> The patch is completely mechanical and can be seen here
>>> <https://reviews.llvm.org/D55557>. It only moves the files
and updates
>>> all references.
>>>
>>> We'd like to hear if there are any things comments/objections
to this
>>> change.
>>>
>>> Thanks !
>>>
>>> *note: We did this before llvm-mca was released and were using a
>>> different simulator, but the idea remains the same.
>>>
>>>
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On 12/12/18 6:51 AM, Andrea Di Biagio via llvm-dev wrote:
Thanks Clement for working on this.

I like the idea of moving the core abstractions of llvm-mca in llvm/lib, as it
potentially enables a number of interesting use cases and future developments.

As you wrote, the patch is very simple (a pretty mechanical change).
From my point of view, this all looks good. Let see if other people have the
same opinion on this.


+1

 -Hal


-Andrea


On Wed, Dec 12, 2018 at 11:58 AM Clement Courbet <courbet at
google.com<mailto:courbet at google.com>> wrote:

(on the correct mailing list)

Hi all,


tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
create a new MCA library in LLVM.


llvm-mca has recently been
split<https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and
the tool part.

  *   The core part simulates the execution of a basic block of machine
instructions as modeled by the llvm SchedModel.

  *   The tool part deals with the plumbing and interacting with the user.


The core part can be used by parts of LLVM that deal with cost modeling (e.g.
scheduling and vectorization). MCA provides a more realistic target for
optimization than the heuristics typically used to drive these passes. We think
that using approaches based on fine-grained cost modeling can greatly improve
the performance of critically hot code, by trading compile time for performance.


As an example of how MCA can be used to improve scheduling, we have built a
prototype machine scheduler that optimizes the simulated latency of a block of
code under the constraints of the scheduling DAG. We've had interesting wins
of 2-3% on assembly kernels for
webp<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
and gemmlowp<https://github.com/google/gemmlowp/pull/91>*.


The patch is completely mechanical and can be seen
here<https://reviews.llvm.org/D55557>. It only moves the files and updates
all references.


We'd like to hear if there are any things comments/objections to this
change.

Thanks !


*note: We did this before llvm-mca was released and were using a different
simulator, but the idea remains the same.

On Wed, Dec 12, 2018 at 11:44 AM Clement Courbet <courbet at
google.com<mailto:courbet at google.com>> wrote:

Hi all,


tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA and
create a new MCA library in LLVM.


llvm-mca has recently been
split<https://bugs.llvm.org/show_bug.cgi?id=37696> into its core part and
the tool part.

  *   The core part simulates the execution of a basic block of machine
instructions as modeled by the llvm SchedModel.

  *   The tool part deals with the plumbing and interacting with the user.


The core part can be used by parts of LLVM that deal with cost modeling (e.g.
scheduling and vectorization). MCA provides a more realistic target for
optimization than the heuristics typically used to drive these passes. We think
that using approaches based on fine-grained cost modeling can greatly improve
the performance of critically hot code, by trading compile time for performance.


As an example of how MCA can be used to improve scheduling, we have built a
prototype machine scheduler that optimizes the simulated latency of a block of
code under the constraints of the scheduling DAG. We've had interesting wins
of 2-3% on assembly kernels for
webp<https://github.com/webmproject/libwebp/commit/67748b41dbb21a43e88f2b6ddf6117f4338873a3>
and gemmlowp<https://github.com/google/gemmlowp/pull/91>*.


The patch is completely mechanical and can be seen
here<https://reviews.llvm.org/D55557>. It only moves the files and updates
all references.


We'd like to hear if there are any things comments/objections to this
change.

Thanks !


*note: We did this before llvm-mca was released and were using a different
simulator, but the idea remains the same.




_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory
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+1.  Great work!

                            -David

Andrea Di Biagio via llvm-dev <llvm-dev at lists.llvm.org> writes:
> Thanks Clement for working on this.
>
> I like the idea of moving the core abstractions of llvm-mca in
> llvm/lib, as it potentially enables a number of interesting use cases
> and future developments.
>
> As you wrote, the patch is very simple (a pretty mechanical change).
> From my point of view, this all looks good. Let see if other people
> have the same opinion on this.
>
> -Andrea
>
> On Wed, Dec 12, 2018 at 11:58 AM Clement Courbet <courbet at
google.com>
> wrote:
>
>         (on the correct mailing list)
>
>     
>         Hi all,
>
>     tl;dr: We'd like to propose moving tools/llvm-mca/lib into lib/MCA
>     and create a new MCA library in LLVM.
>
>     llvm-mca has recently been split into its core part and the tool
>     part.
>
>     *       The core part simulates the execution of a basic block of
>       machine instructions as modeled by the llvm SchedModel.
>
>     *       The tool part deals with the plumbing and interacting with
>       the user.
>
>     The core part can be used by parts of LLVM that deal with cost
>     modeling (e.g. scheduling and vectorization). MCA provides a more
>     realistic target for optimization than the heuristics typically
>     used to drive these passes. We think that using approaches based
>     on fine-grained cost modeling can greatly improve the performance
>     of critically hot code, by trading compile time for performance.
>
>     As an example of how MCA can be used to improve scheduling, we
>     have built a prototype machine scheduler that optimizes the
>     simulated latency of a block of code under the constraints of the
>     scheduling DAG. We've had interesting wins of 2-3% on assembly
>     kernels for webp and gemmlowp*.
>
>     The patch is completely mechanical and can be seen here. It only
>     moves the files and updates all references.
>
>     We'd like to hear if there are any things comments/objections to
>     this change.
>
>     Thanks !
>
>     *note: We did this before llvm-mca was released and were using a
>     different simulator, but the idea remains the same.
>
>     
>     On Wed, Dec 12, 2018 at 11:44 AM Clement Courbet
>     <courbet at google.com> wrote:
>     
>     
>                 Hi all,
>
>         tl;dr: We'd like to propose moving tools/llvm-mca/lib into
>         lib/MCA and create a new MCA library in LLVM.
>
>         llvm-mca has recently been split into its core part and the
>         tool part.
>
>         *           The core part simulates the execution of a basic
>           block of machine instructions as modeled by the llvm
>           SchedModel.
>
>         *           The tool part deals with the plumbing and
>           interacting with the user.
>
>         The core part can be used by parts of LLVM that deal with cost
>         modeling (e.g. scheduling and vectorization). MCA provides a
>         more realistic target for optimization than the heuristics
>         typically used to drive these passes. We think that using
>         approaches based on fine-grained cost modeling can greatly
>         improve the performance of critically hot code, by trading
>         compile time for performance.
>
>         As an example of how MCA can be used to improve scheduling, we
>         have built a prototype machine scheduler that optimizes the
>         simulated latency of a block of code under the constraints of
>         the scheduling DAG. We've had interesting wins of 2-3% on
>         assembly kernels for webp and gemmlowp*.
>
>         The patch is completely mechanical and can be seen here. It
>         only moves the files and updates all references.
>
>         We'd like to hear if there are any things comments/objections
>         to this change.
>
>         Thanks !
>
>         *note: We did this before llvm-mca was released and were using
>         a different simulator, but the idea remains the same.
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev