From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752326Ab2FLGGr (ORCPT ); Tue, 12 Jun 2012 02:06:47 -0400 Received: from e24smtp02.br.ibm.com ([32.104.18.86]:53562 "EHLO e24smtp02.br.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751496Ab2FLGGq (ORCPT ); Tue, 12 Jun 2012 02:06:46 -0400 Date: Tue, 12 Jun 2012 11:36:26 +0530 From: "K.Prasad" To: Peter Zijlstra Cc: Paul Mackerras , Frederic Weisbecker , Ingo Molnar , Arnaldo Carvalho de Melo , Linux Kernel Mailing List , Edjunior Barbosa Machado , "Naveen N. Rao" Subject: Re: [Patch][perf] Invoke __perf_event_disable without an IPI Message-ID: <20120612060626.GB2538@in.ibm.com> Reply-To: prasad@linux.vnet.ibm.com References: <20120611060242.GA2538@in.ibm.com> <1339413213.30462.11.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1339413213.30462.11.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12061206-2194-0000-0000-0000021F79FC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 11, 2012 at 01:13:33PM +0200, Peter Zijlstra wrote: > On Mon, 2012-06-11 at 11:32 +0530, K.Prasad wrote: > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index fd126f8..0e2c1eb 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -1302,6 +1302,7 @@ static int __perf_event_disable(void *info) > > */ > > void perf_event_disable(struct perf_event *event) > > { > > + int ret; > > struct perf_event_context *ctx = event->ctx; > > struct task_struct *task = ctx->task; > > > > @@ -1314,6 +1315,17 @@ void perf_event_disable(struct perf_event *event) > > } > > > > retry: > > + /* > > + * perf_event_disable may be called when interrupts are disabled. > > + * For e.g. hw_breakpoint_handler exception in PowerPC. Hence using > > + * IPIs to invoke __perf_event_disable is not always suitable. When > > + * possible invoke __perf_event_disable directly. > > + */ > > + if ((task_cpu(task) == smp_processor_id()) && irqs_disabled()) { > > Urgh.. > > So what's the callchain for the ppc->hw_bp->perf that triggers this? Hardware breakpoints for user-space have traditionally operated in a one-shot mode i.e. breakpoint is disabled after the first hit by invoking perf_event_disable from hw_breakpoint_handler. PowerPC server class processors follow 'trigger-before-execute', wherein the breakpoint exception is triggered before the instruction performing the memory access is executed. So the one-shot mode prevents the processor from entering an infinite loop and the debugging tools like GDB re-enable the breakpoints explicitly after a SIGTRAP. Thanks, K.Prasad