Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Re: New nanosecond stat patch for 2.5.44 | Date | 30 Oct 2002 16:34:42 -0800 |
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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.
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