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
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