Messages in this thread | | | Date | Tue, 20 Sep 2005 12:24:20 -0700 | From | Scott Lampert <> | Subject | Re: [discuss] Re: [PATCH] x86-64: Fix bad assumption that dualcore cpus have synced TSCs |
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Langsdorf, Mark wrote:
>>On Mon, 2005-09-19 at 21:49 +0200, Andi Kleen wrote: >> >> >>>On Mon, Sep 19, 2005 at 12:42:16PM -0700, john stultz wrote: >>> >>> >>>>On Mon, 2005-09-19 at 21:31 +0200, Andi Kleen wrote: >>>> >>>> >>>>>On Mon, Sep 19, 2005 at 12:16:43PM -0700, john stultz wrote: >>>>> >>>>> >>>>>> This patch should resolve the issue seen in >>>>>> >>>>>> >>bugme bug #5105, >> >> >>>>>>where it is assumed that dualcore x86_64 systems have synced >>>>>>TSCs. This is not the case, and alternate timesources >>>>>> >>>>>> >>should be >> >> >>>>>>used instead. >>>>>> >>>>>> >>>>>I asked AMD some time ago and they told me it was synchronized. >>>>>The TSC on K8 is C state invariant, but not P state >>>>> >>>>> >>invariant, but >> >> >>>>>P states always happen synchronized on dual cores. >>>>> >>>>>So I'm not quite convinced of your explanation yet. >>>>> >>>>> >>>>Would a litter userspace test checking the TSC >>>> >>>> >>synchronization maybe >> >> >>>>shed additional light on the issue? >>>> >>>> >>>Sure you can try it. >>> >>> >>So, bugzilla.kernel.org has (temporarily at least) lost the >>reports from yesterday, but from the email i got, folks using >>my TSC consistency check that I posted were seeing what >>appears to be unsynched TSCs on dualcore AMD systems. >> >> > >My understanding was that each TSC on a dual-core processor >will advance individually and atomically. They will not >always be in synchronization. > > > >>Personally I suspect that the powernow driver is putting the >>cores independently into low power sleep and the TSCs are >>being independently halted, causing them to become unsynchronized. >> >> > >The powernow-k8 driver doesn't know what a low power sleep state >is, so I strongly doubt it is involved here. It only handles >pstates. > >-Mark Langsdorf >K8 PowerNow! Maintainer >AMD, Inc. > > >
Just to add some end-user input here, I see the same issues regardless of whether I'm running with the powernow-k8 or not. The clock problems seem to be unrelated to that, at least on my system. -Scott - 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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