From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752591AbaEVBHA (ORCPT ); Wed, 21 May 2014 21:07:00 -0400 Received: from mx9.pku.edu.cn ([162.105.129.172]:32972 "EHLO mail.pku.edu.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750796AbaEVBG7 convert rfc822-to-8bit (ORCPT ); Wed, 21 May 2014 21:06:59 -0400 X-Spam-Flag: NO X-Spam-Score: -307.494 Date: Thu, 22 May 2014 09:06:46 +0800 (CST) From: =?utf-8?B?566h6Zuq5rab?= To: Chen Gang Cc: gerrit@erg.abdn.ac.uk, Guan Xuetao , David Miller , dccp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <579164883.46799.1400720806850.JavaMail.root@bj-mail03.pku.edu.cn> In-Reply-To: <537D4C73.40901@gmail.com> Subject: =?utf-8?Q?=E5=9B=9E=E5=A4=8D=EF=BC=9A_Re:_=E5=9B=9E=E5=A4=8D=EF=BC=9A_?= =?utf-8?Q?[PATCH_linux-?= =?utf-8?Q?next]_net/dccp/timer.c:_us?= =?utf-8?Q?e_'u64'_instead_of_'s64'_to_avoid_compiler's_warning?= MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Originating-IP: [162.105.129.123] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- Chen Gang 写道： > On 05/22/2014 08:26 AM, 管雪涛 wrote: > > > > ----- Chen Gang 写道： > >> 'dccp_timestamp_seed' is initialized once by ktime_get_real() in > >> dccp_timestamping_init(). It is always less than ktime_get_real() > >> in dccp_timestamp(). > >> > >> Then, ktime_us_delta() in dccp_timestamp() will always return positive > >> number. So can use manual type cast to let compiler and do_div() know > >> about it to avoid warning. > >> > >> The related warning (with allmodconfig under unicore32): > >> > >> CC [M] net/dccp/timer.o > >> net/dccp/timer.c: In function ‘dccp_timestamp’: > >> net/dccp/timer.c:285: warning: comparison of distinct pointer types lacks a cast > >> > >> > >> Signed-off-by: Chen Gang > >> --- > >> net/dccp/timer.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/net/dccp/timer.c b/net/dccp/timer.c > >> index 16f0b22..1cd46a3 100644 > >> --- a/net/dccp/timer.c > >> +++ b/net/dccp/timer.c > >> @@ -280,7 +280,7 @@ static ktime_t dccp_timestamp_seed; > >> */ > >> u32 dccp_timestamp(void) > >> { > >> - s64 delta = ktime_us_delta(ktime_get_real(), dccp_timestamp_seed); > >> + u64 delta = (u64)ktime_us_delta(ktime_get_real(), dccp_timestamp_seed); > > > > Do you assume that delta should be very small? > > Otherwise, return value will be different if data type is changed. > > > > 'u64' is a very very large number. after calculation, if it is based on > nano second (although I am not quite sure whether it is based on it). > > a hour, 3,600,000,000,000ns > a day, 90,000,000,000,000ns > a year, 50,000,000,000,000,000ns > 10 years, 500,000,000,000,000,000ns > 100 years, 5,000,000,000,000,000,000ns > 4G * 4G = 16,000,000,000,000,000,000ns > > So we can assume it will never overflow for 'u64'. However, return value of dccp_timestamp function is u32. > > > Thanks. > -- > Chen Gang > > Open, share, and attitude like air, water, and life which God blessed