From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from nikam.ms.mff.cuni.cz (nikam.ms.mff.cuni.cz [195.113.20.16]) by sourceware.org (Postfix) with ESMTPS id 0EC043857805 for ; Fri, 23 Apr 2021 17:20:59 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 0EC043857805 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=ucw.cz Authentication-Results: sourceware.org; spf=none smtp.mailfrom=hubicka@kam.mff.cuni.cz Received: by nikam.ms.mff.cuni.cz (Postfix, from userid 16202) id 84BAB282612; Fri, 23 Apr 2021 19:20:57 +0200 (CEST) Date: Fri, 23 Apr 2021 19:20:57 +0200 From: Jan Hubicka To: Martin =?iso-8859-2?Q?Li=B9ka?= Cc: Richard Biener , Xinliang David Li , "gcc@gcc.gnu.org" , Eugene Rozenfeld Subject: Re: State of AutoFDO in GCC Message-ID: <20210423172057.GB82007@kam.mff.cuni.cz> References: <62330f82-201d-af7d-d1ed-1c8c529cc0f7@suse.cz> <20210422222906.GB5803@kam.mff.cuni.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Spam-Status: No, score=-8.2 required=5.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, KAM_DMARC_STATUS, KAM_LAZY_DOMAIN_SECURITY, KAM_SHORT, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 23 Apr 2021 17:21:00 -0000 > Hi. > > The current situation is that AutoFDO doesn't work with pretty simple test-cases > we have in testsuite: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71672 > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81379 > > These are ~5 years old and nothing has happened. > > I'm pretty sure the current autofdo can't emit a .gcda file format that > I've changed in the recent years. I believe that the gcda files consumed by auto-FDO are not really sharing the normal gcov file format, just the low level i/o. See read_profile in auto-profile.c. Honza > > > > > I think if we want to keep the feature it makes sense to provide create_gcov > > functionality either directly from perf (input data producer) or from gcc > > (data consumer). Of course I have no idea about its complexity, license > > or implementation language ... > > For me, it's just an i386 feature (maybe aarch64 has perf counters too?), supported > only by vendor (Intel) and I'm not planning working on that. > I don't like having a feature that is obviously broken and potential GCC users get > bad experience every time they try to use it. > > Can we at least deprecate the feature for GCC 11? If these is enough interest, > we can fix it, if not, I would remove it in GCC 13 timeframe. > > Thoughts? > Martin > > > > > Having the tool third-party makes keeping the whole chain working more > > difficult. > > > > Richard. > > > >> Thanks, > >> > >> David > >> > >> On Thu, Apr 22, 2021 at 3:29 PM Jan Hubicka wrote: > >> > >>>> On 4/22/21 9:58 PM, Eugene Rozenfeld via Gcc wrote: > >>>>> GCC documentation for AutoFDO points to create_gcov tool that converts > >>> perf.data file into gcov format that can be consumed by gcc with > >>> -fauto-profile (https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html, > >>> https://gcc.gnu.org/wiki/AutoFDO/Tutorial). > >>>>> > >>>>> I noticed that the source code for create_gcov has been deleted from > >>> https://github.com/google/autofdo on April 7. I asked about that change > >>> in that repo and got the following reply: > >>>>> > >>>>> https://github.com/google/autofdo/pull/107#issuecomment-819108738 > >>>>> > >>>>> "Actually we didn't use create_gcov and havn't updated create_gcov for > >>> years, and we also didn't have enough tests to guarantee it works (It was > >>> gcc-4.8 when we used and verified create_gcov). If you need it, it is > >>> welcomed to update create_gcov and add it to the respository." > >>>>> > >>>>> Does this mean that AutoFDO is currently dead in gcc? > >>>> > >>>> Hello. > >>>> > >>>> Yes. I know that even basic test cases have been broken for years in the > >>> GCC. > >>>> It's new to me that create_gcov was removed. > >>>> > >>>> I tend to send patch to GCC that will remove AutoFDO from GCC. > >>>> I known Bin spent some time working on AutoFDO, has he came up to > >>> something? > >>> > >>> The GCC side of auto-FDO is not that hard. We have most of > >>> infrastructure in place, but stopping point for me was always difficulty > >>> to get gcov-tool working. If some maintainer steps up, I think I can > >>> fix GCC side. > >>> > >>> I am bit unsure how important feature it is - we have FDO that works > >>> quite well for most users but I know there are some users of the LLVM > >>> implementation and there is potential to tie this with other hardware > >>> events to asist i.e. if conversion (where one wants to know how well CPU > >>> predicts the jump rather than just the jump probability) which I always > >>> found potentially interesting. > >>> > >>> Honza > >>>> > >>>> Martin > >>>> > >>>>> > >>>>> Thanks, > >>>>> > >>>>> Eugene > >>>>> > >>>> > >>> >