From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752153AbaCFJpZ (ORCPT ); Thu, 6 Mar 2014 04:45:25 -0500 Received: from mx0.aculab.com ([213.249.233.131]:39815 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751837AbaCFJpU (ORCPT ); Thu, 6 Mar 2014 04:45:20 -0500 From: David Laight To: "'Sukadev Bhattiprolu'" , "Arnaldo Carvalho de Melo" CC: Michael Ellerman , "linux-kernel@vger.kernel.org" , Stephane Eranian , "linuxppc-dev@ozlabs.org" , Paul Mackerras , Jiri Olsa Subject: RE: [PATCH 3/3] perf: Use 64-bit value when comparing sample_regs Thread-Topic: [PATCH 3/3] perf: Use 64-bit value when comparing sample_regs Thread-Index: AQHPOPa0HhCuRKR9rUmCkUl46/2MdZrTzNeQ Date: Thu, 6 Mar 2014 09:44:47 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6D3983@AcuExch.aculab.com> References: <1394080919-17957-1-git-send-email-sukadev@linux.vnet.ibm.com> <1394080919-17957-4-git-send-email-sukadev@linux.vnet.ibm.com> In-Reply-To: <1394080919-17957-4-git-send-email-sukadev@linux.vnet.ibm.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id s269jWua024446 From: Sukadev Bhattiprolu > When checking whether a bit representing a register is set in > sample_regs, a 64-bit mask, use 64-bit value (1LL). > > Signed-off-by: Sukadev Bhattiprolu > --- > tools/perf/util/unwind.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c > index 742f23b..2b888c6 100644 > --- a/tools/perf/util/unwind.c > +++ b/tools/perf/util/unwind.c > @@ -396,11 +396,11 @@ static int reg_value(unw_word_t *valp, struct regs_dump *regs, int id, > { > int i, idx = 0; > > - if (!(sample_regs & (1 << id))) > + if (!(sample_regs & (1LL << id))) > return -EINVAL; > > for (i = 0; i < id; i++) { > - if (sample_regs & (1 << i)) > + if (sample_regs & (1LL << i)) > idx++; > } There are much faster ways to count the number of set bits, especially if you might need to check a significant number of bits. There might even be a function defined somewhere to do it. Basically you just add up the bits, for 16 bit it would be: val = (val & 0x5555) + (val >> 1) & 0x5555; val = (val & 0x3333) + (val >> 2) & 0x3333; val = (val & 0x0f0f) + (val >> 4) & 0x0f0f; val = (val & 0x00ff) + (val >> 8) & 0x00ff; As the size of the work increases the improvement is more significant. (Some of the later masking can probably be proven unnecessary.) David {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I