On 05/22/2014 08:26 AM, 管雪涛 wrote:
>
> ----- Chen Gang <gang.chen.5i5j@xxxxxxxxx> 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 <gang.chen.5i5j@xxxxxxxxx>
>> ---
>> 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
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