llvm dev - Jul 2014 - [LLVMdev] RFC - A tool to convert profiles from external profilers

A few weeks ago, I announced the availability of a conversion tool that
converts Linux Perf sample profiles to LLVM's sample profiler (
https://github.com/google/autofdo).

I have now ported this tool to the LLVM tree, so it can be made available
as part of LLVM. I've got a working version, but I still need to massage
the code to use LLVM's own libraries (logging, flags, etc) and adapt it to
LLVM's coding guidelines.

I expect to have an initial patch ready in a few days. In the meantime, I
would like to open it up for some bike shedding on how this tool will
integrate with LLVM. I cannot guarantee that I'll agree to address all
feedback myself, but I do want to make sure that the major issues and
direction are addressed.

The tool receives two inputs: a profile file and an ELF executable (built
with -gmlt). It produces as output a profile in the format expected by
-fprofile-sample-use.

The requirements on the input is that we must be able to map counts to
specific source file locations. So, the profiling source must be some kind
of sample-based instruction execution counter. Anything that keeps track of
how frequently a specific instruction has been executed.

Using the executable's line table information, the tool maps instruction
locations back to source locations.

Currently, the native profile reader for Linux Perf and the writer for
LLVM's profile are part of the same tree. They both reside in
llvm/tools/llvm-prof-converter.

I would like to support more than Linux Perf, eventually. So, I'm thinking
that I want to move the LLVM profile writer to llvm/lib/ProfileData and
only have the various readers under llvm/tools/llvm-prof-converter.

I don't think I will be working on supporting anything other than Linux
Perf for now. But if anyone is interested in supporting profilers in other
platforms, please let me know. I want to make sure the implementation
doesn't tie itself too much to Linux Perf.


Thanks. Diego.
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Diego Novillo <dnovillo at google.com> writes:
> A few weeks ago, I announced the availability of a conversion tool that
> converts Linux Perf sample profiles to LLVM's sample profiler (https://
> github.com/google/autofdo).
>
> I have now ported this tool to the LLVM tree, so it can be made available
as
> part of LLVM. I've got a working version, but I still need to massage
the code
> to use LLVM's own libraries (logging, flags, etc) and adapt it to
LLVM's
> coding guidelines.
>
> I expect to have an initial patch ready in a few days. In the meantime, I
> would like to open it up for some bike shedding on how this tool will
> integrate with LLVM. I cannot guarantee that I'll agree to address all
> feedback myself, but I do want to make sure that the major issues and
> direction are addressed.
Sounds great! Thanks for working on this.
> The tool receives two inputs: a profile file and an ELF executable (built
with
> -gmlt). It produces as output a profile in the format expected by
> -fprofile-sample-use.
Do you have a plan in mind on how this will decide between input profile
file formats once there are options other than perf? The two obvious
approaches are autodetection/a format flag or having a different
profile-converter tool per format. I think I'm in favour of the former.
> The requirements on the input is that we must be able to map counts to
> specific source file locations. So, the profiling source must be some kind
of
> sample-based instruction execution counter. Anything that keeps track of
how
> frequently a specific instruction has been executed.
>
> Using the executable's line table information, the tool maps
instruction
> locations back to source locations.
>
> Currently, the native profile reader for Linux Perf and the writer for
LLVM's
> profile are part of the same tree. They both reside in llvm/tools/
> llvm-prof-converter.
>
> I would like to support more than Linux Perf, eventually. So, I'm
thinking
> that I want to move the LLVM profile writer to llvm/lib/ProfileData and
only
> have the various readers under llvm/tools/llvm-prof-converter.
This sounds like the right direction to me. Arguably, the readers could
go into lib/ProfileData as well, leaving only the tool logic under
llvm/tools. I think either split would be fine.
> I don't think I will be working on supporting anything other than Linux
Perf
> for now. But if anyone is interested in supporting profilers in other
> platforms, please let me know. I want to make sure the implementation
doesn't
> tie itself too much to Linux Perf.
>
> Thanks. Diego.

On 07/16/2014 11:20 AM, Diego Novillo wrote:
>
> A few weeks ago, I announced the availability of a conversion tool 
> that converts Linux Perf sample profiles to LLVM's sample profiler 
> (https://github.com/google/autofdo).
This seems like a potentially useful tool.  I support having this in
tree.
> I would like to support more than Linux Perf, eventually. So, I'm 
> thinking that I want to move the LLVM profile writer to 
> llvm/lib/ProfileData and only have the various readers under 
> llvm/tools/llvm-prof-converter. 
Given we now have multiple proposed users, having these libraries in 
some shared location seems reasonable.  I would want both the readers & 
writers in the same location.

Glancing at the current code in ProfileData, I do not see any uses in 
LLVM itself.  There is one checked-in use in the tools directory.   I'm 
hesitant about putting support code for tools which is not otherwise 
used in the main llvm source tree.  Is there a better place we could put 
this?  (Or am I simply being too conservative?)

We do need to make a clear distinction between externally defined 
formats (with test cases! and spec references!) and internally defined 
formats which can be changed.

Philip

> On Jul 16, 2014, at 11:20 AM, Diego Novillo <dnovillo at google.com>
wrote:
> 
> 
> A few weeks ago, I announced the availability of a conversion tool that
converts Linux Perf sample profiles to LLVM's sample profiler
(https://github.com/google/autofdo).
> 
> I have now ported this tool to the LLVM tree, so it can be made available
as part of LLVM. I've got a working version, but I still need to massage the
code to use LLVM's own libraries (logging, flags, etc) and adapt it to
LLVM's coding guidelines.
> 
> I expect to have an initial patch ready in a few days. In the meantime, I
would like to open it up for some bike shedding on how this tool will integrate
with LLVM. I cannot guarantee that I'll agree to address all feedback
myself, but I do want to make sure that the major issues and direction are
addressed.
> 
> The tool receives two inputs: a profile file and an ELF executable (built
with -gmlt). It produces as output a profile in the format expected by
-fprofile-sample-use.
> 
> The requirements on the input is that we must be able to map counts to
specific source file locations. So, the profiling source must be some kind of
sample-based instruction execution counter. Anything that keeps track of how
frequently a specific instruction has been executed.
> 
> Using the executable's line table information, the tool maps
instruction locations back to source locations.
> 
> Currently, the native profile reader for Linux Perf and the writer for
LLVM's profile are part of the same tree. They both reside in
llvm/tools/llvm-prof-converter.
What do you think about invoking this via the existing “llvm-profdata” tool?  It
currently supports two commands: “show” and “merge”. We could add a new
“convert” command.
> 
> I would like to support more than Linux Perf, eventually. So, I'm
thinking that I want to move the LLVM profile writer to llvm/lib/ProfileData and
only have the various readers under llvm/tools/llvm-prof-converter.
> 
> I don't think I will be working on supporting anything other than Linux
Perf for now. But if anyone is interested in supporting profilers in other
platforms, please let me know. I want to make sure the implementation
doesn't tie itself too much to Linux Perf.
> 
> 
> Thanks. Diego.
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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On Wed, Jul 16, 2014 at 3:34 PM, Justin Bogner <mail at justinbogner.com>
wrote:
> Do you have a plan in mind on how this will decide between input profile
> file formats once there are options other than perf? The two obvious
> approaches are autodetection/a format flag or having a different
> profile-converter tool per format. I think I'm in favour of the former.
Initially a format flag (--type={perf,text,...}). It's easier to
implement than autodetection, which can always be added later.

> This sounds like the right direction to me. Arguably, the readers could
> go into lib/ProfileData as well, leaving only the tool logic under
> llvm/tools. I think either split would be fine.
Yeah. I am splitting the tool, so the Perf reader goes into its own
library in llvm/lib/PerfReader (or somesuch) and the driver goes in
llvm/tools.

I quite liked Bob's idea of adding functionality to the existing
llvm-profdata driver. Seems natural to add a --convert flag to it.


Diego.

On Fri, Jul 18, 2014 at 8:30 PM, Bob Wilson <bob.wilson at apple.com>
wrote:
> What do you think about invoking this via the existing “llvm-profdata”
tool?
> It currently supports two commands: “show” and “merge”. We could add a new
> “convert” command.
I had not thought of that, but I think it makes perfect sense. I'll
drop my current driver and move the logic into llvm-profdata. Thanks
for the suggestion.


Diego.