On 2022/5/17 09:03, Tejun Heo wrote: > On Tue, May 17, 2022 at 08:57:55AM +0800, Chengming Zhou wrote: >> #define time_after64(a,b) \ >> (typecheck(__u64, a) && \ >> typecheck(__u64, b) && \ >> ((__s64)((b) - (a)) < 0)) >> #define time_before64(a,b) time_after64(b,a) >> >> I still don't get why my changes are wrong. :-) > > It's a wrapping timestamp where a lower value doesn't necessarily mean > earlier. The before/after relationship is defined only in relation to each > other. Imagine a cirle representing the whole value range and picking two > spots in the circle, if one is in the clockwise half from the other, the > former is said to be earlier than the latter and vice-versa. vtime runs way > faster than nanosecs and wraps regularly, so we can't use absolute values to > compare before/after. Yes, thanks for the explanation. But the problem is not comparing two timestamp, since ioc->margins.target is not a timestamp. This patch just fix a corner case when now->vnow < ioc->margins.target: u64 vtarget; vtarget = now->vnow - ioc->margins.target; --> vtarget should be a timestamp earlier than vnow. But when now->vnow < ioc->margins.target, vtarget would be a timestamp after vnow. Thanks. > > Thanks. >
