From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752293AbbABR0P (ORCPT ); Fri, 2 Jan 2015 12:26:15 -0500 Received: from mail-pa0-f45.google.com ([209.85.220.45]:46883 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750772AbbABR0O (ORCPT ); Fri, 2 Jan 2015 12:26:14 -0500 Message-ID: <54A6D4B2.9070609@gmail.com> Date: Fri, 02 Jan 2015 10:26:10 -0700 From: David Ahern User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Shaohua Li CC: Peter Zijlstra , Andy Lutomirski , "linux-kernel@vger.kernel.org" , X86 ML , Kernel-team@fb.com, "H. Peter Anvin" , Ingo Molnar , John Stultz Subject: Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO References: <95a7ba1a95a6251439d5ca2d3d56fe7f0778cb95.1418857018.git.shli@fb.com> <20141219112350.GJ30905@twins.programming.kicks-ass.net> <20141219170334.GM30905@twins.programming.kicks-ass.net> <20150102025953.GA1253265@devbig257.prn2.facebook.com> <54A6B9D5.5040804@gmail.com> <20150102170223.GA2381637@devbig257.prn2.facebook.com> <54A6D0B6.7090700@gmail.com> <20150102171738.GB2381637@devbig257.prn2.facebook.com> In-Reply-To: <20150102171738.GB2381637@devbig257.prn2.facebook.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/2/15 10:17 AM, Shaohua Li wrote: > On Fri, Jan 02, 2015 at 10:09:10AM -0700, David Ahern wrote: >> On 1/2/15 10:02 AM, Shaohua Li wrote: >>> On Fri, Jan 02, 2015 at 08:31:33AM -0700, David Ahern wrote: >>>> On 1/1/15 7:59 PM, Shaohua Li wrote: >>>>> I'm wondering how we could use the perf to implament a clock_gettime. >>>>> reading the perf fd or using ioctl is slow so reading the mmap >>>>> ringbuffer is the only option. But as far as I know the ringbuffer has >>>>> data only when an event is generated. Between two events, there is >>>>> nothing we can read from the ringbuffer. Then how can application get >>>>> time info in the interval? >>>> >>>> Are you wanting to read perf_clock from userspace? >>> >>> Yep, in some sort of form. Basically I want to read the time a task >>> runs. Peter suggests we can read the activation time of a perf event. >>> But I don't want to use any system call, as it's slow and likes >>> clock_gettime. >> >> Since we cannot get the capability committed upstream a number of >> folks are using this method: >> >> https://github.com/dsahern/linux/blob/perf-full-monty/README.ahern >> >> ie., a KLM exports perf_clock and apps can use: >> >> #define CLOCK_PERF 14 >> if (clock_gettime(CLOCK_PERF, &ts) != 0) { >> } >> >> No vdso acceleration, but works with an unmodified kernel. > > no, that's not what I want. as I said, we don't want any syscall (unless > it's vdso based). A number of clocks are vdso based (e.g., CLOCK_MONOTONIC). Those are not good enough? David