Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751877Ab2HPLXv (ORCPT ); Thu, 16 Aug 2012 07:23:51 -0400 Received: from ozlabs.org ([203.10.76.45]:47569 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751213Ab2HPLXu (ORCPT ); Thu, 16 Aug 2012 07:23:50 -0400 From: Michael Neuling To: Peter Zijlstra cc: K Prasad , Frederic Weisbecker , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Ingo Molnar Subject: Re: powerpc/perf: hw breakpoints return ENOSPC In-reply-to: <1345102812.31459.114.camel@twins> References: <28857.1345091034@neuling.org> <1345102812.31459.114.camel@twins> Comments: In-reply-to Peter Zijlstra message dated "Thu, 16 Aug 2012 09:40:12 +0200." X-Mailer: MH-E 8.2; nmh 1.3; GNU Emacs 23.3.1 Date: Thu, 16 Aug 2012 21:17:29 +1000 Message-ID: <20344.1345115849@neuling.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1341 Lines: 36 Peter, > > On this second syscall, fetch_bp_busy_slots() sets slots.pinned to be 1, > > despite there being no breakpoint on this CPU. This is because the call > > the task_bp_pinned, checks all CPUs, rather than just the current CPU. > > POWER7 only has one hardware breakpoint per CPU (ie. HBP_NUM=1), so we > > return ENOSPC. > > I think this comes from the ptrace legacy, we register a breakpoint on > all cpus because when we migrate a task it cannot fail to migrate the > breakpoint. > > Its one of the things I hate most about the hwbp stuff as it relates to > perf. > > Frederic knows more... Maybe I should wait for Frederic to respond but I'm not sure I understand what you're saying. I can see how using ptrace hw breakpoints and perf hw breakpoints at the same time could be a problem, but I'm not sure how this would stop it. Are you saying that we need to keep at least 1 slot free at all times, so that we can use it for ptrace? Is "perf record -e mem:0x10000000 true" ever going to be able to work on POWER7 with only one hw breakpoint resource per CPU? Thanks, Mikey -- 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/