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Re: AutoFDO profile toolchain is open-sourced
- From: Ilya Palachev <i dot palachev at samsung dot com>
- To: Xinliang David Li <davidxl at google dot com>, Jan Hubicka <hubicka at ucw dot cz>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Vyacheslav Barinov <v dot barinov at samsung dot com>, Diego Novillo <dnovillo at google dot com>, Sebastian Pop <sebpop at gmail dot com>, Dehao Chen <dehao at google dot com>
- Date: Fri, 08 May 2015 12:00:16 +0300
- Subject: Re: AutoFDO profile toolchain is open-sourced
- Authentication-results: sourceware.org; auth=none
- References: <CAO2gOZWydpiBXb=1QDyCRt-ybDieqy8X4S_+uRZk2Y2v+cFdYQ at mail dot gmail dot com> <5523ED98 dot 8080007 at samsung dot com> <CAFk3UF8To5Qcz8NN5rUF3z6j8CCg_89A+62P=1U9YrtbZ5=mLg at mail dot gmail dot com> <20150410203927 dot GA18980 at atrey dot karlin dot mff dot cuni dot cz> <CAAkRFZ+2RK=-qKo4eCRmq0N1QjENm0tAe2PbX3xnC76UyuFrJA at mail dot gmail dot com> <CAAkRFZLMP3SvGZqCdyLbnZqfY6RUqwRJ3tpVRYKMA+ZCVt2u9A at mail dot gmail dot com> <20150410224327 dot GA87750 at kam dot mff dot cuni dot cz> <CAAkRFZJ4MPCqCMJ7z9WK50e3HPJWnmZHoiWU0m-e2b915GSU9g at mail dot gmail dot com>
On 11.04.2015 01:49, Xinliang David Li wrote:
Suppose that I have no opportunity to collect profile on x86
architecture with LBR support and the only available architecture is
arm/aarch64 (since the application code is significantly different when
compiled for different architectures because of manual optimizations and
different function names and structure).
On Fri, Apr 10, 2015 at 3:43 PM, Jan Hubicka <firstname.lastname@example.org> wrote:
LBR is used for both cfg edge profiling and indirect call Target value
I see, that makes sense ;) I guess if we want to support profile collection
on targets w/o this feature we could still use one of the algorithms that
try to guess edge profile from BB profile.
Our experience with sampling cycles or retired instructions to guess
BB profile has not been great -- the profile quality is significantly
worse than LBR (which can almost match instrumentation based profile).
Honza has mentioned that it's possible to guess edge profile from BB
profile. How do you think, can this help in the above described situation?
Yes, this will be much worse than LBR, but can it give any performance
benefit compared with no edge profile at all?