Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933133AbdGKO1U (ORCPT ); Tue, 11 Jul 2017 10:27:20 -0400 Received: from foss.arm.com ([217.140.101.70]:45676 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932820AbdGKO1R (ORCPT ); Tue, 11 Jul 2017 10:27:17 -0400 Date: Tue, 11 Jul 2017 15:26:18 +0100 From: Mark Rutland To: Ingo Molnar Cc: Kyle Huey , gregkh@linuxfoundation.org, Peter Zijlstra , Vince Weaver , "Jin, Yao" , stable@vger.kernel.org, Alexander Shishkin , Arnaldo Carvalho de Melo , Jiri Olsa , Linus Torvalds , Namhyung Kim , Stephane Eranian , Thomas Gleixner , acme@kernel.org, jolsa@kernel.org, kan.liang@intel.com, Will Deacon , open list , "Robert O'Callahan" Subject: Re: [PATCH] perf/core: generate overflow signal when samples are dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the kernel in the "skid" region) Message-ID: <20170711142618.GF2681@leverpostej> References: <20170628105600.GC5981@leverpostej> <20170628174900.GG8252@leverpostej> <20170704090313.xyb5lntyy55ga7dm@hirez.programming.kicks-ass.net> <20170704093345.GB19649@leverpostej> <20170704102159.GB20062@leverpostej> <20170711090358.6si4un4guz6dbxkz@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170711090358.6si4un4guz6dbxkz@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1792 Lines: 38 On Tue, Jul 11, 2017 at 11:03:58AM +0200, Ingo Molnar wrote: > > * Kyle Huey wrote: > > > On Wed, Jul 5, 2017 at 10:07 PM, Robert O'Callahan wrote: > > > On Tue, Jul 4, 2017 at 3:21 AM, Mark Rutland wrote: > > >> Should any of those be moved into the "should be dropped" pile? > > > > > > Why not be conservative and clear every sample you're not sure about? > > > > > > We'd appreciate a fix sooner rather than later here, since rr is > > > currently broken on every stable Linux kernel and our attempts to > > > implement a workaround have failed. > > > > > > (We have separate "interrupt" and "measure" counters, and I thought we > > > might work around this regression by programming the "interrupt" > > > counter to count kernel events as well as user events (interrupting > > > early is OK), but that caused our (completely separate) "measure" > > > counter to report off-by-one results (!), which seems to be a > > > different bug present on a range of older kernels.) > > > > This seems to have stalled out here unfortunately. > > > > Can we get a consensus (from ingo or peterz?) on Mark's question? Or, > > alternatively, can we move the patch at the top of this thread forward > > on the stable branches until we do reach an answer to that question? > > > > We've abandoned hope of working around this problem in rr and are > > currently broken for all of our users with an up-to-date kernel, so > > the situation for us is rather dire at the moment I'm afraid. > > Sorry about that - I've queued up a revert for the original commit and will send > the fix to Linus later today. I've added a -stable tag as well so it can be > forwarded to Greg the moment it hits upstream. Thanks for handling this. Mark.