Messages in this thread |  | | | From | James Cleverdon <> | | Subject | Re: do_gettimeofday vs. rdtsc in the scheduler | | Date | Tue, 17 Sep 2002 15:55:52 -0700 |
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On Tuesday 17 September 2002 03:38 pm, David S. Miller wrote: > From: Andi Kleen <ak@suse.de> > Date: Wed, 18 Sep 2002 00:44:42 +0200 > > > I don't know how Sun and SGI manage with their larger systems. Either > > they don't do clock sync, or they may have to make expensive > > tradeoffs. > > I guess you could always run NTP between the different CPUs ;) ;) > > :-) > > More seriously, you don't need to have the cpu tick registers sync'd, > it is the rate that matters. > > Once booted, you can sync these system tick registers with a pretty > straight forward algorithm in the kernel. Bonus points if you can > figure out how to cancel out the cost of moving the system tick sample > cachelines between master and slave in your algorithm :-)
Been there. Done that. Had the product canceled. ;^)
The initial sync was easy, even with variable latencies on cache lines. A much simplified NTP-ish algorithm works fine. The painful thing was bus clock drift and programs that foolishly relied on the TSC being the same between CPUs and between nodes.
-- James Cleverdon IBM xSeries Linux Solutions {jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot 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/
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