From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 917C22FB6; Mon, 24 Jul 2023 21:29:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4513C433C7; Mon, 24 Jul 2023 21:29:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690234174; bh=fqARBeO4c2YTPeSk975Ka86xirYABo69PGISN4e7vLI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=N3HQrz3JW8g3YO8EdzbLFeYf1mrY/Yawvo/WMzv/qkz0xPca4NstPDjimzDip1S8g nw39gZSxGmRk/c/9EDQOdKC1OGyX0djizdVuLTFy8KdUOepoE2r2QCo6LPi8AD08Hf I5w0NF6wY0diODvSoN3fyDgk+6D5S64SEsHYiv3OB+W2o7cXiOsjJnm0IotuaSmVnJ 6ZlSQq/eTQX9HFXKx64wcF/CL79FgOW4P3qpBw22LbkCPDDCgX2G3omtzW7DLv1HNO 63kpv6ofoqyMXwxEHg7/ihcB3grujPrtFNhHaB7FDlWXrZRAP344c3DSU2ZU9/Zhkk e3QuQhHl45esQ== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 22F5240516; Mon, 24 Jul 2023 18:29:31 -0300 (-03) Date: Mon, 24 Jul 2023 18:29:31 -0300 From: Arnaldo Carvalho de Melo To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Adrian Hunter , Nathan Chancellor , Nick Desaulniers , Tom Rix , Kan Liang , Yang Jihong , Ravi Bangoria , Carsten Haitzler , Zhengjun Xing , James Clark , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, llvm@lists.linux.dev, maskray@google.com Subject: Re: [PATCH v1 0/4] Perf tool LTO support Message-ID: References: <20230724201247.748146-1-irogers@google.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230724201247.748146-1-irogers@google.com> X-Url: http://acmel.wordpress.com Em Mon, Jul 24, 2023 at 01:12:43PM -0700, Ian Rogers escreveu: > Add a build flag, LTO=1, so that perf is built with the -flto > flag. Address some build errors this configuration throws up. > > For me on my Debian derived OS, "CC=clang CXX=clang++ LD=ld.lld" works > fine. With GCC LTO this fails with: > ``` > lto-wrapper: warning: using serial compilation of 50 LTRANS jobs > lto-wrapper: note: see the ‘-flto’ option documentation for more information > /usr/bin/ld: /tmp/ccK8kXAu.ltrans10.ltrans.o:(.data.rel.ro+0x28): undefined reference to `memset_orig' > /usr/bin/ld: /tmp/ccK8kXAu.ltrans10.ltrans.o:(.data.rel.ro+0x40): undefined reference to `__memset' > /usr/bin/ld: /tmp/ccK8kXAu.ltrans10.ltrans.o:(.data.rel+0x28): undefined reference to `memcpy_orig' > /usr/bin/ld: /tmp/ccK8kXAu.ltrans10.ltrans.o:(.data.rel+0x40): undefined reference to `__memcpy' > /usr/bin/ld: /tmp/ccK8kXAu.ltrans44.ltrans.o: in function `test__arch_unwind_sample': > /home/irogers/kernel.org/tools/perf/arch/x86/tests/dwarf-unwind.c:72: undefined reference to `perf_regs_load' > collect2: error: ld returned 1 exit status > ``` > > The issue is that we build multiple .o files in a directory and then > link them into a .o with "ld -r" (cmd_ld_multi). This early link step > appears to trigger GCC to remove the .S file definition of the symbol > and break the later link step (the perf-in.o shows perf_regs_load, for > example, going from the text section to being undefined at the link > step which doesn't happen with clang or without LTO). It is possible > to work around this by taking the final perf link command and adding > the .o files generated from .S back into it, namely: > arch/x86/tests/regs_load.o > bench/mem-memset-x86-64-asm.o > bench/mem-memcpy-x86-64-asm.o > > A quick performance check and the performance improvements from LTO > are noticeable: > > Non-LTO > ``` > $ perf bench internals synthesize > # Running 'internals/synthesize' benchmark: > Computing performance of single threaded perf event synthesis by > synthesizing events on the perf process itself: > Average synthesis took: 202.216 usec (+- 0.160 usec) > Average num. events: 51.000 (+- 0.000) > Average time per event 3.965 usec > Average data synthesis took: 230.875 usec (+- 0.285 usec) > Average num. events: 271.000 (+- 0.000) > Average time per event 0.852 usec > ``` > > LTO > ``` > $ perf bench internals synthesize > # Running 'internals/synthesize' benchmark: > Computing performance of single threaded perf event synthesis by > synthesizing events on the perf process itself: > Average synthesis took: 104.530 usec (+- 0.074 usec) > Average num. events: 51.000 (+- 0.000) > Average time per event 2.050 usec > Average data synthesis took: 112.660 usec (+- 0.114 usec) > Average num. events: 273.000 (+- 0.000) > Average time per event 0.413 usec Cool stuff! Applied locally, test building now on the container suite. - Arnaldo > ``` > > Ian Rogers (4): > perf stat: Avoid uninitialized use of perf_stat_config > perf parse-events: Avoid use uninitialized warning > perf test: Avoid weak symbol for arch_tests > perf build: Add LTO build option > > tools/perf/Makefile.config | 5 +++++ > tools/perf/tests/builtin-test.c | 11 ++++++++++- > tools/perf/tests/stat.c | 2 +- > tools/perf/util/parse-events.c | 2 +- > tools/perf/util/stat.c | 2 +- > 5 files changed, 18 insertions(+), 4 deletions(-) > > -- > 2.41.0.487.g6d72f3e995-goog > -- - Arnaldo