From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753639Ab3LJQa5 (ORCPT ); Tue, 10 Dec 2013 11:30:57 -0500 Received: from mail-wi0-f169.google.com ([209.85.212.169]:49561 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751313Ab3LJQa4 (ORCPT ); Tue, 10 Dec 2013 11:30:56 -0500 Date: Tue, 10 Dec 2013 17:30:53 +0100 From: Frederic Weisbecker To: Oleg Nesterov Cc: suravee.suthikulpanit@amd.com, mingo@kernel.org, mingo@redhat.com, jacob.w.shin@gmail.com, a.p.zijlstra@chello.nl, acme@ghostprotocols.net, hpa@zytor.com, tgl@domain.invalid, linux-kernel@vger.kernel.org, sherry.hurwitz@amd.com Subject: Re: [PATCH 1/3] perf/x86/amd: AMD support for bp_len > HW_BREAKPOINT_LEN_8 Message-ID: <20131210163051.GI10633@localhost.localdomain> References: <1380730268-25807-1-git-send-email-suravee.suthikulpanit@amd.com> <1380730268-25807-2-git-send-email-suravee.suthikulpanit@amd.com> <20131210152342.GE10633@localhost.localdomain> <20131210161945.GA23086@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131210161945.GA23086@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 10, 2013 at 05:19:45PM +0100, Oleg Nesterov wrote: > On 12/10, Frederic Weisbecker wrote: > > > > On Wed, Oct 02, 2013 at 11:11:06AM -0500, suravee.suthikulpanit@amd.com wrote: > > > @@ -279,7 +260,16 @@ static int arch_build_bp_info(struct perf_event *bp) > > > } > > > > > > /* Len */ > > > + info->mask = 0; > > > + > > > switch (bp->attr.bp_len) { > > > + default: > > > + if (!is_power_of_2(bp->attr.bp_len)) > > > + return -EINVAL; > > > + if (!cpu_has_bpext) > > > + return -EOPNOTSUPP; > > > + info->mask = bp->attr.bp_len - 1; > > > + /* fall through */ > > > > So, that's perhaps just personal preference but having the default on > > top of the switch makes things very confusing. Can't we put the above > > in the end of the switch instead? > > Then "fall through" won't work ;) Indeed, now may be that's just me but it's very hard to parse :) There are other ways to perform the above, it's no big deal if we duplicate one line of code. > > > > @@ -314,11 +303,11 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp) > > > if (ret) > > > return ret; > > > > > > - ret = -EINVAL; > > > - > > > switch (info->len) { > > > case X86_BREAKPOINT_LEN_1: > > > align = 0; > > > + if (info->mask) > > > + align = info->mask; > > > > Confused, I thought mask is set only when length is above 8? > > Yes. But we need the info->len for hw anyway. if mask != 0 then > len == X86_BREAKPOINT_LEN_1 and it is still used by encode_dr7(). > Note that it is not the length in bytes, it is the magic x86 code. Good point, and that matches the above fallthrough. Thanks. > > ->bp_len is the length. > > Oleg. >