Date: Wed, 29 Jul 2015 18:35:02 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, vikas.shivappa@intel.com, x86@kernel.org,
        hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org, tj@kernel.org,
        matt.fleming@intel.com, will.auld@intel.com,
        glenn.p.williamson@intel.com, kanaka.d.juvva@intel.com
Subject: Re: [PATCH 9/9] x86/intel_rdt: Intel haswell Cache Allocation
 enumeration
Message-ID: <20150729163502.GY25159@twins.programming.kicks-ass.net>
References: <1435789270-27010-1-git-send-email-vikas.shivappa@linux.intel.com>
 <1435789270-27010-10-git-send-email-vikas.shivappa@linux.intel.com>
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On Wed, Jul 01, 2015 at 03:21:10PM -0700, Vikas Shivappa wrote:
> +	boot_cpu_data.x86_cache_max_closid = 4;
> +	boot_cpu_data.x86_cache_max_cbm_len = 20;

That's just vile. And I'm surprised it even works, I would've expected
boot_cpu_data to be const.

So the CQM code has paranoid things like:

	max_rmid = MAX_INT;
	for_each_possible_cpu(cpu)
		max_rmid = min(max_rmid, cpu_data(cpu)->x86_cache_max_rmid);

And then uses max_rmid. This has the advantage that if you mix parts in
a multi-socket environment and hotplug socket 0 to a later part which a
bigger {rm,clos}id your allocation isn't suddenly too small.

Please do similar things and only ever look at cpu_data once, at init
time.
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