linux-kernel - Re: [PATCH v2 22/33] x86/intel_rdt.c: Extend RDT to per cache and per resources

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Date:   Tue, 13 Sep 2016 15:54:38 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>, Borislav Petkov <bp@...e.de>,
        Stephane Eranian <eranian@...gle.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Shaohua Li <shli@...com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 22/33] x86/intel_rdt.c: Extend RDT to per cache and per
 resources

On 09/08/2016 02:57 AM, Fenghua Yu wrote:
> +static int __init rdt_setup(char *str)
> +{
> +	char *tok;
> +
> +	while ((tok = strsep(&str, ",")) != NULL) {
> +		if (!*tok)
> +			return -EINVAL;
> +
> +		if (strcmp(tok, "simulate_cat_l3") == 0) {
> +			pr_info("Simulate CAT L3\n");
> +			rdt_opts.simulate_cat_l3 = true;
> +		} else if (strcmp(tok, "disable_cat_l3") == 0) {
> +			pr_info("CAT L3 is disabled\n");
> +			disable_cat_l3 = true;
> +		} else {
> +			pr_info("Invalid rdt option\n");
> +			return -EINVAL;
> +		}
> +	}
> +
> +	return 0;
> +}
> +__setup("resctrl=", rdt_setup);

So, this allows you to specify both simulation and disabling at the same
time, and in the same option?  That seems a bit screwy, plus it requires
some parsing which is quite prone to being broken.  How about just
having two setup options:

__setup("resctrl=simulate_cat_l3", rdt_setup...);
__setup("resctrl=disable_cat_l3", rdt_setup...);

And allow folks to specify "resctrl" more than once instead of requiring
the comma-separated arguments?  Then you don't have to do any parsing at
all and your __setup() handlers become one-liners.

Is "resctrl" really the best name for this sucker?  Wouldn't
"intel-rdt=" or something be nicer?

Also, a lot of __setup() functions actually clear cpuid bits.  Should
this be clearing X86_FEATURE_CAT_L3 instead of keeping a boolean around
that effectively overrides it?

> +static inline bool cat_l3_supported(struct cpuinfo_x86 *c)
> +{
> +	if (cpu_has(c, X86_FEATURE_CAT_L3))
> +		return true;
> +
> +	/*
> +	 * Probe for Haswell server CPUs.
> +	 */
> +	if (c->x86 == 0x6 && c->x86_model == 0x3f)
> +		return cache_alloc_hsw_probe();
> +
> +	return false;
> +}

#include <asm/intel-family.h> and s/0x3f/INTEL_FAM6_HASWELL_X/, please.
 Then your comment even go away.