From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752683AbaEVBBr (ORCPT ); Wed, 21 May 2014 21:01:47 -0400 Received: from mail-pb0-f53.google.com ([209.85.160.53]:44593 "EHLO mail-pb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752139AbaEVBBp (ORCPT ); Wed, 21 May 2014 21:01:45 -0400 Message-ID: <537D4C73.40901@gmail.com> Date: Thu, 22 May 2014 09:01:39 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: =?UTF-8?B?566h6Zuq5rab?= CC: gerrit@erg.abdn.ac.uk, Guan Xuetao , David Miller , dccp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: =?UTF-8?B?5Zue5aSN77yaIFtQQVRDSCBsaW51eC1uZXh0XSBuZXQvZGNjcC8=?= =?UTF-8?B?dGltZXIuYzogdXNlICd1NjQnIGluc3RlYWQgb2YgJ3M2NCcgdG8gYXZvaWQgY28=?= =?UTF-8?B?bXBpbGVyJ3Mgd2FybmluZw==?= References: <1546102096.46113.1400718399706.JavaMail.root@bj-mail03.pku.edu.cn> In-Reply-To: <1546102096.46113.1400718399706.JavaMail.root@bj-mail03.pku.edu.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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'. Thanks. -- Chen Gang Open, share, and attitude like air, water, and life which God blessed