Re: [PATCH v3 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs

[Peter Zijlstra]

On Thu, Nov 06, 2014 at 12:23:21PM +0000, Matt Fleming wrote:
> +/*
> + * If we fail to assign a new RMID for intel_cqm_rotation_rmid because
> + * cachelines are still tagged with RMIDs in limbo, we progressively
> + * increment the threshold until we find an RMID in limbo with <=
> + * __intel_cqm_threshold lines tagged. This is designed to mitigate the
> + * problem where cachelines tagged with an RMID are not steadily being
> + * evicted.
> + *
> + * On successful rotations we decrease the threshold back towards zero.
> + *
> + * __intel_cqm_max_threshold provides an upper bound on the threshold,
> + * and is measured in bytes because it's exposed to userland.
> + */
> +static unsigned int __intel_cqm_threshold;
> +static unsigned int __intel_cqm_max_threshold = -1;

Should we initialize that to a finite value? Surely results are absolute
crap if we do indeed reach that max?
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