Followup to: <20021030221724.GA25231@bjl1.asuk.net>
By author: Jamie Lokier <lk@tantalophile.demon.co.uk>
In newsgroup: linux.dev.kernel
>
> That's some of the overhead. The other overhead is reading the clock,
> which is quite high on x86 when TSC is not available. On a Pentium
> with no reliable TSC, I think that the time for a read() system call
> is comparable to the time to read the clock.
>
Typically the way you deal with not having a usably cheap
nanosecond-resolution clock is that you use the best available clock
(say if HZ=1000 you'll increment by 1000000 each timer tick), and then
simply use an atomic counter for the smaller divisions. This makes
the relation "is A newer than B" correct, while avoiding the overhead
of producing exact timestamps below the available resolution.
-hpa
-- <hpa@transmeta.com> at work, <hpa@zytor.com> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt <amsp@zytor.com> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:50 EST