Re: RFC: Standalone AutoFDO Profile Tool for GCC

Jan Hubička via Gcc <[email protected]> writes:

> On Thu, Apr 23, 2026 at 1:09 AM Kugan Vivekanandarajah <
> [email protected]> wrote:
>
>> Hi,
>>
>> Building on our discussions from the last Cauldron, we propose creating a
>> native, simplified AutoFDO tool for GCC to replace our current reliance on
>> external Google tools which is not actively maintained. I'll follow up with
>> a detailed design document as soon as we have a consensus on the proposal.
>>
>
> Thank you for writting it. In my opinion the tool is really needed to make
> AutoFDO practically useful, so I hope it will happen this stage 1 :)
>
>>
>> Thanks,
>> Kugan
>>
>> Summary
>> =======
>>
>> We propose a standalone, minimal tool for generating AutoFDO profiles
>> that can be consumed by the GCC AutoFDO toolchain, with the goal of
>> integrating it into the GCC repository. The tool would
>> support: (1) offline read existing perf.data (single-process or
>> system-wide) and produce a profile for a target binary; (2) direct
>> attach to a process via the PMU (LBR or BRBE / SPE), bypassing perf
>> record and building the profile from the live sample stream; (3)
>>
> I think this is quite important missing feature of the existing tool.  With
> branch history, It is hard to balance
> the setting to keep profile good while avoiding too large perf.data file.
> Data used by
> GCC is much smaller.
>
>> - Current AutoFDO tools (e.g. from Google) are not widely used with
>> GCC. LLVM has a similar profile-creation tool integrated with the
>> compiler. A tightly coupled tool for GCC would allow for easy
>> development and upgradation.
>>
> I also wonder if there is a chance for collaboration/integration with perf
> tools itself.
> In particular, the current tool is picky about perf.data file format that
> is not completely
> stable. So perhaps the perf.data loading can be sharing a library with
> perftools.
> On the other hand hwoever minimizing dependencies is quite important.

I think Andi had https://github.com/andikleen/perf-gcov.

>
> Honza
>
>>
>>

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