Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752644AbbBRSVw (ORCPT ); Wed, 18 Feb 2015 13:21:52 -0500 Received: from mail-ob0-f173.google.com ([209.85.214.173]:32849 "EHLO mail-ob0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752129AbbBRSVv (ORCPT ); Wed, 18 Feb 2015 13:21:51 -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> <54E4D5C4.1070005@gmail.com> Date: Wed, 18 Feb 2015 13:21:50 -0500 Message-ID: Subject: Re: [PATCH v2 4/4] clock: add perf_clock posix clock From: Stephane Eranian To: John Stultz Cc: David Ahern , 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 , 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: 2080 Lines: 39 On Wed, Feb 18, 2015 at 1:18 PM, John Stultz wrote: > On Wed, Feb 18, 2015 at 10:11 AM, David Ahern wrote: >> On 2/18/15 11:00 AM, John Stultz wrote: >>> >>> 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? >> >> >> AFAIK Stephane is not proposing this patch for inclusion but rather it is an >> unfortunate necessary evil. The module exposes perf_clock (ie., local_clock) >> to userspace and allows in this case the generation of samples with a perf >> timestamp which is required for proper sorting. >> >> I understand this solution is not liked, but it works, requires no kernel >> modifications to achieve the end goal and can be used for kernels going back >> to at least 2.6.38 (perhaps earlier, have not checked). > > Yep. And I'm sympathetic to the fact that an alternative solution > hasn't made it upstream yet. I'm hopeful Pawel's recent approach will > make it in (it seems like it hasn't raised any flags w/ scheduler > folks - but I've not always been able to follow the discussion > closely). > Ok, let me try switching my series to Pawel's patch then. Should not take long. -- 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/