From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752048Ab3KSAYw (ORCPT ); Mon, 18 Nov 2013 19:24:52 -0500 Received: from lgeamrelo01.lge.com ([156.147.1.125]:42790 "EHLO LGEAMRELO01.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751418Ab3KSAYu (ORCPT ); Mon, 18 Nov 2013 19:24:50 -0500 X-AuditID: 9c93017d-b7b24ae000002834-ce-528aafd0cf4d From: Namhyung Kim To: Ingo Molnar Cc: Peter Zijlstra , David Ahern , Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, jolsa@redhat.com, Frederic Weisbecker , Mike Galbraith , Stephane Eranian Subject: Re: [PATCH 4/5] perf record: mmap output file - v5 References: <1384267617-3446-1-git-send-email-dsahern@gmail.com> <1384267617-3446-5-git-send-email-dsahern@gmail.com> <20131112145707.GV5056@laptop.programming.kicks-ass.net> <20131112150751.GA19321@ghostprotocols.net> <20131112151944.GX5056@laptop.programming.kicks-ass.net> <52824AE3.4050207@gmail.com> <20131112211121.GC25913@gmail.com> <20131113113439.GI21461@twins.programming.kicks-ass.net> <52864ED1.1080607@gmail.com> <20131118090117.GE3866@twins.programming.kicks-ass.net> <20131118094036.GA26251@gmail.com> Date: Tue, 19 Nov 2013 09:24:48 +0900 In-Reply-To: <20131118094036.GA26251@gmail.com> (Ingo Molnar's message of "Mon, 18 Nov 2013 10:40:36 +0100") Message-ID: <877gc5utkf.fsf@sejong.aot.lge.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ingo, On Mon, 18 Nov 2013 10:40:36 +0100, Ingo Molnar wrote: > * Peter Zijlstra wrote: > >> On Fri, Nov 15, 2013 at 09:41:53AM -0700, David Ahern wrote: >> > On 11/13/13, 4:34 AM, Peter Zijlstra wrote: >> > >>>one option here is not allow page faults and system wide system calls. >> > >>>system wide tracing needs mmap; page faults for a task can use write(). >> > >>>I left that option in case something like this came up. >> > >> >> > >>So maybe splice() sounds like the right long term solution after all? :-/ >> > > >> > >Right until you put a tracepoint (kprobe) somewhere in whatever function >> > >is used to transfer a single page into/from a splice pipe. >> > > >> > >You can always screw yourself over using this stuff, no exceptions. >> > > >> > >> > What now? Can we add the mmap path as an option? >> >> I'd say an option is always a possibility, but someone please try >> what happens if you use stupid large events (dwarf stack copies) on >> PERF_COUNT_SW_PAGE_FAULTS (.period=1) while recording with mmap(). >> >> The other option is to simply disallow PERF_SAMPLE_STACK_USER for >> that event. >> >> Personally I think 8k copies for every event are way stupid anyway, >> that's a metric ton of data at a huge cost. > > Well, with 1 khz sampling of a single threaded workload it's 8MB per > second - that's 80 MB for 10 seconds profiling - not the end of the > world. We now use 4 khz sampling frequency by default, just FYI. :) Thanks, Namhyung