From: Ulf Samuelsson <ulf.samuelsson@ericsson•com>
To: <netdev@vger•kernel.org>
Subject: RFC: Use of "jiffies" vs "jiffies64" in the neighbour system.
Date: Wed, 25 Mar 2015 11:11:45 +0100 [thread overview]
Message-ID: <551289E1.8090609@ericsson.com> (raw)
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....
--
Best Regards,
Ulf Samuelsson
next reply other threads:[~2015-03-25 10:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-25 10:11 Ulf Samuelsson [this message]
2015-03-25 10:27 ` RFC: Use of "jiffies" vs "jiffies64" in the neighbour system Michal Kubecek
2015-03-25 12:35 ` Ulf Samuelsson
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