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Date:   Thu, 20 Sep 2018 16:11:15 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Reinette Chatre <reinette.chatre@intel.com>
Cc:     tglx@linutronix.de, fenghua.yu@intel.com, tony.luck@intel.com,
        mingo@redhat.com, acme@kernel.org, gavin.hindman@intel.com,
        jithu.joseph@intel.com, dave.hansen@intel.com, hpa@zytor.com,
        x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V5 5/6] x86/intel_rdt: Use perf infrastructure for
 measurements
Message-ID: <20180920141115.GX24124@hirez.programming.kicks-ass.net>
References: <cover.1537377064.git.reinette.chatre@intel.com>
 <d31d652432a62e770fc971d3e6fe59faa9e65413.1537377064.git.reinette.chatre@intel.com>
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On Wed, Sep 19, 2018 at 10:29:10AM -0700, Reinette Chatre wrote:
> +static int measure_l3_residency(void *_plr)
> +{

> +	counts.miss_after -= counts.miss_before;
> +	if (boot_cpu_data.x86_model == INTEL_FAM6_BROADWELL_X) {
> +		/*
> +		 * On BDW references and misses are counted, need to adjust.
> +		 * Sometimes the "hits" counter is a bit more than the
> +		 * references, for example, x references but x + 1 hits.
> +		 * To not report invalid hit values in this case we treat
> +		 * that as misses equal to references.
> +		 */
> +		/* First compute the number of cache references measured */
> +		counts.hits_after -= counts.hits_before;

> +		/* Next convert references to cache hits */
> +		counts.hits_after -= counts.miss_after > counts.hits_after ?
> +					counts.hits_after : counts.miss_after;

Maybe:
		counts.hits_after -= min(counts.hits_after, counts.miss_after);