Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752295AbbBRSP2 (ORCPT ); Wed, 18 Feb 2015 13:15:28 -0500 Received: from mail-ie0-f179.google.com ([209.85.223.179]:44764 "EHLO mail-ie0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751701AbbBRSP1 (ORCPT ); Wed, 18 Feb 2015 13:15:27 -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 10:15:26 -0800 Message-ID: Subject: Re: [PATCH v2 4/4] clock: add perf_clock posix clock From: John Stultz To: Stephane Eranian 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: 2157 Lines: 50 On Wed, Feb 18, 2015 at 10:10 AM, Stephane Eranian wrote: > 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). I believe it can be found here: https://lkml.org/lkml/2015/1/21/711 thanks -john -- 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/