From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754039Ab2HPXeL (ORCPT ); Thu, 16 Aug 2012 19:34:11 -0400 Received: from ozlabs.org ([203.10.76.45]:38927 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752507Ab2HPXeJ (ORCPT ); Thu, 16 Aug 2012 19:34:09 -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: <1345117498.29668.23.camel@twins> References: <28857.1345091034@neuling.org> <1345102812.31459.114.camel@twins> <20344.1345115849@neuling.org> <1345117498.29668.23.camel@twins> Comments: In-reply-to Peter Zijlstra message dated "Thu, 16 Aug 2012 13:44:58 +0200." X-Mailer: MH-E 8.2; nmh 1.3; GNU Emacs 23.3.1 Date: Fri, 17 Aug 2012 09:34:07 +1000 Message-ID: <8649.1345160047@neuling.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > > 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. > > ptrace uses perf for hwbp support so we're stuck with all kinds of > stupid ptrace constraints.. or somesuch. OK > > Are you saying that we need to keep at least 1 slot free at all times, > > so that we can use it for ptrace? > > No, I'm saying perf-hwbp is weird because of ptrace, maybe the ptrace > weirdness shouldn't live in perf-hwpb but in the ptrace-perf glue > however.. OK. > > Is "perf record -e mem:0x10000000 true" ever going to be able to work on > > POWER7 with only one hw breakpoint resource per CPU? > > I think it should work... but I'm fairly sure it currently doesn't > because of how things are done. 'perf record -ie mem:0x100... true' > might just work. Adding -i doesn't help. Mikey