linux-kernel - Re: [PATCH v2 08/33] x86/intel_rdt: Add Class of service management

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Message-ID: <alpine.DEB.2.20.1609081037020.5647@nanos>
Date:   Thu, 8 Sep 2016 10:56:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     "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>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 08/33] x86/intel_rdt: Add Class of service
 management

On Thu, 8 Sep 2016, Fenghua Yu wrote:
> @@ -0,0 +1,12 @@
> +#ifndef _RDT_H_
> +#define _RDT_H_

The standard guard is

    _ASM_X86_RDT_H

> +
> +#ifdef CONFIG_INTEL_RDT

What's the purpose of sticking a struct definition inside an ifdef?

> +
> +struct clos_cbm_table {
> +	unsigned long cbm;
> +	unsigned int clos_refcnt;

Please proper align the struct members for readability sake

	unsigned long	cbm;
	unsigned int	clos_refcnt;

Adding a kerneldoc comment above the struct explaining it would not hurting
either.

> +/*
> + * cctable maintains 1:1 mapping between CLOSid and cache bitmask.
> + */
> +static struct clos_cbm_table *cctable;
> +/*
> + * closid availability bit map.
> + */
> +unsigned long *closmap;
> +static DEFINE_MUTEX(rdtgroup_mutex);
> +
> +static inline void closid_get(u32 closid)
> +{
> +	struct clos_cbm_table *cct = &cctable[closid];
> +
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	cct->clos_refcnt++;

So the whole thing can be written with a single line at the single call
site.

	cc_table[closid].clos_refcnt++;

And that already has the lockdep_assert_held() check. While companies might
pay based on line counts, kernel development asks for readable and sensible
code.

> +}
> +
> +static int closid_alloc(u32 *closid)
> +{
> +	u32 maxid;
> +	u32 id;

Please put variables with the same type into one line. There is no value in
wasting screen estate.

> +
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	maxid = boot_cpu_data.x86_cache_max_closid;
> +	id = find_first_zero_bit(closmap, maxid);
> +	if (id == maxid)
> +		return -ENOSPC;
> +
> +	set_bit(id, closmap);
> +	closid_get(id);
> +	*closid = id;
> +
> +	return 0;
> +}
> +
> +static inline void closid_free(u32 closid)
> +{
> +	clear_bit(closid, closmap);
> +	cctable[closid].cbm = 0;
> +}
> +
> +static void closid_put(u32 closid)
> +{
> +	struct clos_cbm_table *cct = &cctable[closid];
> +
> +	lockdep_assert_held(&rdtgroup_mutex);
> +	if (WARN_ON(!cct->clos_refcnt))
> +		return;
> +
> +	if (!--cct->clos_refcnt)
> +		closid_free(closid);
> +}
>  
>  static int __init intel_rdt_late_init(void)
>  {
>  	struct cpuinfo_x86 *c = &boot_cpu_data;
> +	u32 maxid;
> +	int err = 0, size;
>  
>  	if (!cpu_has(c, X86_FEATURE_CAT_L3))
>  		return -ENODEV;
>  
> -	pr_info("Intel cache allocation detected\n");
> +	maxid = c->x86_cache_max_closid;
>  
> -	return 0;
> +	size = maxid * sizeof(struct clos_cbm_table);
> +	cctable = kzalloc(size, GFP_KERNEL);
> +	if (!cctable) {
> +		err = -ENOMEM;
> +		goto out_err;

I told you that before: Using a goto just to return err is pointless and
silly. What the hell is wrong with 

		return -ENOMEM;
???

> +	}
> +
> +	size = BITS_TO_LONGS(maxid) * sizeof(long);
> +	closmap = kzalloc(size, GFP_KERNEL);
> +	if (!closmap) {
> +		kfree(cctable);
> +		err = -ENOMEM;
> +		goto out_err;

Groan.

> +	}
> +
> +	pr_info("Intel cache allocation enabled\n");
> +out_err: