Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752057AbdGYN1c (ORCPT ); Tue, 25 Jul 2017 09:27:32 -0400 Received: from foss.arm.com ([217.140.101.70]:47282 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751515AbdGYN1b (ORCPT ); Tue, 25 Jul 2017 09:27:31 -0400 Date: Tue, 25 Jul 2017 14:27:38 +0100 From: Will Deacon To: Pratyush Anand Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , huawei.libin@huawei.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2 1/4] hw_breakpoint: Add step_needed event attribute Message-ID: <20170725132737.GC28815@arm.com> References: <9d4f76f3a0bffe93a6d5146c9b53ee7b985f22da.1499416107.git.panand@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9d4f76f3a0bffe93a6d5146c9b53ee7b985f22da.1499416107.git.panand@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3612 Lines: 94 On Fri, Jul 07, 2017 at 05:33:57PM +0530, Pratyush Anand wrote: > Architecture like ARM64 currently allows to use default hw breakpoint > single step handler only to perf. However, some other users like few > systemtap tests or kernel test in > samples/hw_breakpoint/data_breakpoint.c can also work with default step > handler implementation. At the same time, some other like GDB/ptrace may > implement their own step handler. > > Therefore, this patch introduces a new perf_event_attr bit field, so > that arch specific code(specially on arm64) can make a decision to > enable single stepping. > > Any architecture which is not using this field will not have any > side effect. > > Signed-off-by: Pratyush Anand > --- > include/linux/hw_breakpoint.h | 6 ++++++ > include/uapi/linux/perf_event.h | 3 ++- > kernel/events/core.c | 2 ++ > tools/include/uapi/linux/perf_event.h | 3 ++- > 4 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h > index 0464c85e63fd..6173ae048cbc 100644 > --- a/include/linux/hw_breakpoint.h > +++ b/include/linux/hw_breakpoint.h > @@ -38,6 +38,12 @@ static inline int hw_breakpoint_type(struct perf_event *bp) > return bp->attr.bp_type; > } > > +static inline bool > +hw_breakpoint_needs_single_step(struct perf_event *bp) > +{ > + return bp->attr.step_needed; > +} > + > static inline unsigned long hw_breakpoint_len(struct perf_event *bp) > { > return bp->attr.bp_len; > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index b1c0b187acfe..00935808de0d 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -345,7 +345,8 @@ struct perf_event_attr { > context_switch : 1, /* context switch data */ > write_backward : 1, /* Write ring buffer from end to beginning */ > namespaces : 1, /* include namespaces data */ > - __reserved_1 : 35; > + step_needed : 1, /* Use arch step handler */ > + __reserved_1 : 34; This needs documenting properly, as I really have no idea how userspace is going to use it sensibley, especially as you silently overwrite it in some cases below. Will > > union { > __u32 wakeup_events; /* wakeup every n events */ > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 6c4e523dc1e2..220e26941475 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->attr.step_needed = 1; > } else { > event->overflow_handler = perf_event_output_forward; > event->overflow_handler_context = NULL; > + event->attr.step_needed = 1; > } > > perf_event__state_init(event); > diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h > index b1c0b187acfe..00935808de0d 100644 > --- a/tools/include/uapi/linux/perf_event.h > +++ b/tools/include/uapi/linux/perf_event.h > @@ -345,7 +345,8 @@ struct perf_event_attr { > context_switch : 1, /* context switch data */ > write_backward : 1, /* Write ring buffer from end to beginning */ > namespaces : 1, /* include namespaces data */ > - __reserved_1 : 35; > + step_needed : 1, /* Use arch step handler */ > + __reserved_1 : 34; > > union { > __u32 wakeup_events; /* wakeup every n events */ > -- > 2.9.3 >