linux-kernel - Re: [PATCH v4 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs

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Message-ID: <20150107121617.GF25325@worktop.programming.kicks-ass.net>
Date:	Wed, 7 Jan 2015 13:16:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Kanaka Juvva <kanaka.d.juvva@...el.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v4 10/11] perf/x86/intel: Perform rotation on Intel CQM
 RMIDs

On Fri, Nov 14, 2014 at 09:15:11PM +0000, Matt Fleming wrote:
 +	/*
> +	 * A reasonable upper limit on the max threshold is the number
> +	 * of lines tagged per RMID if all RMIDs have the same number of
> +	 * lines tagged in the LLC.
> +	 *
> +	 * For a 35MB LLC and 56 RMIDs, this is ~1.8% of the LLC.
> +	 */
> +	__intel_cqm_max_threshold =
> +		boot_cpu_data.x86_cache_size * 1024 / (cqm_max_rmid + 1);

Seeing how a percentage is without unit, the 35MB figure seems
pointless.

Also, why would a flat distribution be a good measure for 'empty'? I
would think that would in fact constitute in use.

Should we make this 1/16th of this figure or any other random fraction <
1 ?
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