From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932484Ab3LDN4z (ORCPT ); Wed, 4 Dec 2013 08:56:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36658 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932320Ab3LDN4y (ORCPT ); Wed, 4 Dec 2013 08:56:54 -0500 Date: Wed, 4 Dec 2013 14:57:43 +0100 From: Oleg Nesterov To: Frederic Weisbecker Cc: Suravee Suthikulpanit , Ingo Molnar , Ingo Molnar , jacob.w.shin@gmail.com, Peter Zijlstra , Arnaldo Melo , "H. Peter Anvin" , LKML , Sherry Hurwitz Subject: Re: [PATCH 1/3] perf/x86/amd: AMD support for bp_len > HW_BREAKPOINT_LEN_8 Message-ID: <20131204135743.GB7251@redhat.com> References: <1380730268-25807-1-git-send-email-suravee.suthikulpanit@amd.com> <1380730268-25807-2-git-send-email-suravee.suthikulpanit@amd.com> <20131108194122.GA14606@localhost.localdomain> <20131109151156.GA14249@redhat.com> <20131109153236.GE26079@localhost.localdomain> <20131109155428.GA15649@redhat.com> <20131111154417.GD26853@localhost.localdomain> <20131111175131.GA14906@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/03, Frederic Weisbecker wrote: > > 2013/11/11 Oleg Nesterov : > > On 11/11, Frederic Weisbecker wrote: > >> > >> On Sat, Nov 09, 2013 at 04:54:28PM +0100, Oleg Nesterov wrote: > >> > > >> > Up to you and Suravee, but can't we cleanup this later? > >> > > >> > This series was updated many times to address a lot of (sometimes > >> > contradictory) complaints. > >> > >> Sure. But I'm confident that we can solve the conflicting mask / len issue easily beside. > >> I mean, I don't feel confident with merging things as is, otoh it should be easy to fix up. > > > > I do not really understand where do you see the conflict... > > > > I can be easily wrong, but afaics currently mask / len issue is simply > > the implementation detail. > > I think it's like we have an object that has a length, and to create > this object we pass both kilometers and miles. Ok it's a bit different > here because a mask can apply on top of a len. But here it's used to > define essentially the same thing (ie: a range of address) Yes. perf/etc uses length, the current imlementation uses ->mask to actually set the range. > > Actually, mask is more powerfull. And initial versions of this patches > > (iirc) tried to use mask as an argument which comes from the userspace > > (tools/perf, perf_event_attr, etc). But one of reviewers nacked this > > interfacer, so we still use len. > > Well, we can still reconsider it if needed but to me it seems that > mask is only interesting if we may deal with non contiguous range of > addresses. And this is what this mask can actually do. Just there is no way (currently) to pass the mask from userpace. > >> Right but what if we want breakpoints having a size below 8? Like break on instructions > >> from 0x1000 to 0x1008 ? > >> > >> Or should we ignore range instruction breakpoints when len < 8? > > > > In this case the new code has no effect (iirc), we simply use > > X86_BREAKPOINT_LEN_* and "tell the hardware about extended range/mask" > > code is never called. IIRC, currently we simply check bp_mask != 0 > > to distinguish. > > I'm not sure I understand correctly. Do you mean that range below 8 > don't rely on extended breakpoint range? IIRC - yes. > Ideally it would be nice if we drop bp_mask and use extended ranges > only when len > 8. How does that sound? Again, iirc, this is what the code does. except (in essence) it checks mask != 0 instead of len > 8. And yes, we can probably drop bp_mask (unless we are going to support the contiguous ranges), just I think we can do this later. Oleg.