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Date: Wed, 25 Mar 2015 13:35:51 +0100 From: Ulf Samuelsson <ulf.samuelsson@...csson.com> To: Michal Kubecek <mkubecek@...e.cz> CC: <netdev@...r.kernel.org> Subject: Re: RFC: Use of "jiffies" vs "jiffies64" in the neighbour system. On 03/25/2015 11:27 AM, Michal Kubecek wrote: > On Wed, Mar 25, 2015 at 11:11:45AM +0100, Ulf Samuelsson wrote: >> If you run HZ = 1000, then jiffies will wrap around after 49,71 days. >> This means that all time compares in the neighbour system will fail. >> >> From what I can see from "jiffies,h" there is no attempt to detect >> the wrap-around. >> >> #define time_after(a,b) \ >> (typecheck(unsigned long, a) && \ >> typecheck(unsigned long, b) && \ >> ((long)(b) - (long)(a) < 0)) >> #define time_before(a,b) time_after(b,a) >> >> #define time_after_eq(a,b) \ >> (typecheck(unsigned long, a) && \ >> typecheck(unsigned long, b) && \ >> ((long)(a) - (long)(b) >= 0)) >> #define time_before_eq(a,b) time_after_eq(b,a) > I might have misunderstood you but those macros do handle the > wrap-around. For example, with 64-bit long and a = 1, > b = 0xffffffffffffffff, you get > > ((long)(b) - (long)(a)) = (-1) - (1) = -2 < 0 > > so that time_after(1, 0xffffffffffffffff) is true. It will give correct > results as long as the difference is less than half of range of the > type. > > Michal Kubecek > OK, Now I see why it works. Best Regards, Ulf Samuelsson -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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