RFC: Use of "jiffies" vs "jiffies64" in the neighbour system.
Subsystems (2)
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)
While the problem is not big for most users, I suspect it will affect quality at the time of wrap-around.
It looks like garbage collection will stop in neigh_alloc, since time has not passed time of last flush.
reachable time will no longer be recomputed in periodic_work
When you are in REACHABLE state, you will stay there, since "now" will be before "confirmed" +"reachable_time", so the entry will not be moved to DELAY or STALE,
If you are in delay state, you will move the entry into REACHABLE even if you did not get a response.
and so on....
Signature · 2 lines
Best Regards, Ulf Samuelsson
Quoted 10 lines · Ulf Samuelsson
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))
Quoted 7 lines
#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
Quoted 22 lines · Michal Kubecek
Quoted 10 lines · Ulf Samuelsson
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))Quoted 7 lines
#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
Quoted 8 lines
((long)(b) - (long)(a)) = (-1) - (1) = -2 < 0so 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