Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752847AbbBRSLB (ORCPT ); Wed, 18 Feb 2015 13:11:01 -0500 Received: from mail-ob0-f177.google.com ([209.85.214.177]:57268 "EHLO mail-ob0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752583AbbBRSK5 (ORCPT ); Wed, 18 Feb 2015 13:10:57 -0500 MIME-Version: 1.0 In-Reply-To: References: <1424280109-9801-1-git-send-email-eranian@google.com> <1424280109-9801-5-git-send-email-eranian@google.com> Date: Wed, 18 Feb 2015 13:10:56 -0500 Message-ID: Subject: Re: [PATCH v2 4/4] clock: add perf_clock posix clock From: Stephane Eranian To: John Stultz Cc: Linux Kernel Mailing List , Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , "ak@linux.intel.com" , Jiri Olsa , Namhyung Kim , Rose Belcher , Sukadev Bhattiprolu , Sonny Rao , John Mccutchan , David Ahern , Adrian Hunter , Pawel Moll Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1951 Lines: 43 On Wed, Feb 18, 2015 at 1:00 PM, John Stultz wrote: > On Wed, Feb 18, 2015 at 9:21 AM, Stephane Eranian wrote: >> This patch is a re-packaging of David's Ahern >> posix perf clock available here: >> >> https://github.com/dsahern/linux/blob/perf-full-monty/README.ahern >> >> The patch itself is based on Pawel Moll's original post: >> >> https://lkml.org/lkml/2013/3/14/523 >> >> The new clock is call PERF_CLOCK. To use it >> >> #include >> #include >> >> struct timespec ts; >> >> clock_gettime(PERF_CLOCK, &ts); > > I'd still strongly recommend against exposing the perf clock to > userspace this way. The time domain isn't clearly different from > something like CLOCK_MONOTONIC_RAW and doesn't really have well > defined behavior. We're just exporting "whatever the kernel does > internally" to userspace, and in the past similar internal use clocks > like the sched_clock have changed their behavior, so I'm not confident > the perf clock is really baked enough (including cross architectures) > to make it part of the ABI. > > Pawel and others have continued to work on other approaches that allow > for perf events to be interpolated to, or use CLOCK_MONOTONIC itself, > which I don't object to, so you might want to follow up on those? > Personally, I don't have a preference. I want something that is EASY to correlate to the perf_events timestamp and that is PORTABLE across architectures. Where is the patch that uses CLOCK_MONOTONIC? I assume it changes the clock used by perf_events and I further assume this clock can be read from NMI context (without requiring locking). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/