Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751915AbdHAISb (ORCPT ); Tue, 1 Aug 2017 04:18:31 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:43839 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750763AbdHAIS2 (ORCPT ); Tue, 1 Aug 2017 04:18:28 -0400 Date: Tue, 1 Aug 2017 10:18:17 +0200 From: Peter Zijlstra To: Pratyush Anand Cc: linux-arm-kernel@lists.infradead.org, Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , mark.rutland@arm.com, will.deacon@arm.com, huawei.libin@huawei.com, takahiro.akashi@linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/5] hw_breakpoint: Add step_needed event attribute Message-ID: <20170801081817.GG6524@worktop.programming.kicks-ass.net> References: <1d7ca935857f93bd09c82a2ff57a53e373211b7e.1501496603.git.panand@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1d7ca935857f93bd09c82a2ff57a53e373211b7e.1501496603.git.panand@redhat.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1475 Lines: 40 On Mon, Jul 31, 2017 at 04:10:29PM +0530, Pratyush Anand wrote: > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 24a635887f28..7da951f94b47 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -233,6 +233,12 @@ struct hw_perf_event { > */ > u64 freq_time_stamp; > u64 freq_count_stamp; > + /* > + * A HW breakpoint user can either have it's own step handling > + * mechanism or it can use default step handling meachanism defined > + * by arch code. Set step_needed to use default mechanism. > + */ > + int step_needed; You'll note that there is an anonymous structure inside the anonymous union specifically dedicated to hardware breakpoint state. Why not put it there? > #endif > }; > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 6c4e523dc1e2..66ce5574e778 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -9444,9 +9444,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, > } else if (is_write_backward(event)){ > event->overflow_handler = perf_event_output_backward; > event->overflow_handler_context = NULL; > + event->hw.step_needed = 1; > } else { > event->overflow_handler = perf_event_output_forward; > event->overflow_handler_context = NULL; > + event->hw.step_needed = 1; > } These here need a comment, because even if I'd know now why the heck we need that = 1 here, I'd sure as hell won't know tomorrow.