From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Anand K. Mistry" Subject: Re: [PATCH v3] perf record: Use an eventfd to wakeup when done Date: Mon, 25 May 2020 11:43:00 +1000 Message-ID: References: <20200508145624.1.I4d7421c6bbb1f83ea58419082481082e19097841@changeid> <20200513122012.v3.1.I4d7421c6bbb1f83ea58419082481082e19097841@changeid> <87a71y93lr.fsf@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <87a71y93lr.fsf@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Andi Kleen Cc: linux-perf-users@vger.kernel.org, Alexander Shishkin , Arnaldo Carvalho de Melo , Ingo Molnar , Jiri Olsa , Mark Rutland , Namhyung Kim , Peter Zijlstra , linux-kernel@vger.kernel.org List-Id: linux-perf-users.vger.kernel.org On Sat, 23 May 2020 at 23:35, Andi Kleen wrote: > > Anand K Mistry writes: > > } > > > > + done_fd = eventfd(0, EFD_NONBLOCK); > > This will make perf depend on a recent glibc or other library > that implements eventfd. Wouldn't surprise me if some kind > of build time check is needed for this to pass all of Arnaldo's > built tests. Looks like Arnaldo made that change when merging: https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/commit/?h=perf/core&id=e9db221d37f91409040cf7f3fbed08b44e055ae9 This makes me curious. How old a kernel should modern tools support? >From the man page, eventfd was added in 2.6.22 (and eventfd2 in 2.6.27), which was 2007 (or 2008 for eventfd2) and glibc-2.8 which was 2008. I understand the kernel's policy of never breaking userspace, but what about userspace tools? > > > -Andi -- Anand K. Mistry Software Engineer Google Australia