From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen Gang Date: Thu, 22 May 2014 01:01:39 +0000 Subject: Re: =?UTF-8?B?5Zue5aSN77yaIFtQQVRDSCBsaW51eC1uZXh0XSBuZXQvZGNjcC8=?= =?UTF-8?B?dGltZXIuYzogdXNlICd1N Message-Id: <537D4C73.40901@gmail.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: dccp@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