Messages in this thread | | | Date | Thu, 5 Oct 2006 16:31:45 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC] The New and Improved Logdev (now with kprobes!) |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > > On Thu, 5 Oct 2006, Mathieu Desnoyers wrote: > > > > > Just as a detail : LTTng traces NMI, which can happen on top of a > > xtime_lock. So yes, I have to consider the impact of this kind of lock when I > > choose my time source, which is currently a per architecture TSC read, > > or a read of the jiffies counter when the architecture does not have a > > synchronised TSC over the CPUs. This is abstracted in include/asm-*/ltt.h. > > > > I'm curious. How do you show the interactions between two CPUs when the > TSC isn't in sync? Using jiffies is not fast enough to know the order of > events that happen within usecs. >
I shift the jiffies and OR that with a logical clock which increments atomically and is shared across the CPUs. It is slow and ugly, but it works. :)
Mathieu
> -- Steve > > > > I know it doesn't support dynamic ticks, I'm working on using the HRtimers > > instead, but I must make sure that the seqlock read will fail if it nests over > > a write seqlock. > > > > MAthieu > > > > OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg > > Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 > > OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - 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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