Re: [PATCH 2/3] perf/x86/pebs: add workaround for broken OVFL status on HSW

[Andi Kleen <ak@linux.intel.com>]

> +		/*
> +		 * There are cases where, even though, the PEBS ovfl bit is set in
> +		 * GLOBAL_OVF_STATUS, the PEBS events may also have their overflow bits
> +		 * set for their counters. We must clear them here because they have
> +		 * been processed as exact samples in the drain_pebs() routine. They
> +		 * must not be processed again in the for_each_bit_set() loop for
> +		 * regular samples below.
> +		 */
> +		status &= ~cpuc->pebs_enabled;
> +		status &= x86_pmu.intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;

If you just clear the bits here they will not be acked and stay around
forever in GLOBAL_STATUS, which causes other problems.

You need a separate ack_status variable that contains all bits and is always
acked.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only