Re: [PATCH 0/4] x86: Add Cache QoS Monitoring (CQM) support

[H. Peter Anvin]

On 01/12/2014 11:55 PM, Peter Zijlstra wrote:
> 
> The problem is, since there's a limited number of RMIDs we have to
> rotate at some point, but since changing RMIDs is nondeterministic we
> can't.
> 

This is fundamentally the crux here.  RMIDs are quite expensive for the
hardware to implement, so they are limited - but recycling them is
*very* expensive because you literally have to touch every line in the
cache.

	-hpa


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