RE: [Ptools-perfapi] [perfmon2] [PATCH] perf_events: AMD eventscheduling (v1)

From: Peter Zijlstra
Date: Fri Jan 22 2010 - 12:42:39 EST

On Fri, 2010-01-22 at 11:33 -0600, John McCalpin wrote:

> * Think of the system as having four performance monitors per core
> *plus* four performance monitors for the "shared" structures on the
> chip (L3, crossbar, HyperTransport links, memory controllers).

Would have been nice to have them as a separately addressable pmu
instead of shadowing the logical cpu's pmu.

But that's all ancient history of course..

> There is an additional hazard when working with early K8 processors --
> a hardware bug causes the counts of all shared counters to be reset to
> zero any time any shared register is programmed. This makes
> "protecting" users somewhat more difficult....

Could you qualify early k8 a bit more, it shouldn't be hard to add a
quirk for a specific set of cpus to read/reset all counters before
writing to the shared pmu.

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