Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [Patch 1/4] Delay accounting: Initialization | Date | Wed, 16 Nov 2005 02:50:22 +0100 |
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On Wednesday 16 November 2005 02:48, Shailabh Nagar wrote:
> > Are there problems with using sched_clock()for timestamping if one is prepared > to live with them not necessarily being nanosecond accurate ? I'm trying to search > the archives etc. but if you can respond with any quick comments, that'd be very > helpful.
First it can be relatively slow on P4s (hundreds of cycles)
On other systems it can run with different frequencies on different CPUs, so you never need to assume a timestamp from one CPU is comparable with the one from other CPUs (the scheduler carefully avoids this)
If you need a stable timestamp over multiple CPUs don't use it.
In general do_gettimeofday is much safer. do_gettimeofday shouldn't be that much slower for the case where TSC works, and where it doesn't there is no other alternative.
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