Re: [PATCH V15 05/11] x86/intel_rdt: Add Class of service management

[Luiz Capitulino]

On Thu,  1 Oct 2015 23:09:39 -0700
Fenghua Yu <fenghua.yu@xxxxxxxxx> wrote:

> Adds some data-structures and APIs to support Class of service
> management(closid). There is a new clos_cbm table which keeps a 1:1
> mapping between closid and capacity bit mask (cbm)
> and a count of usage of closid. Each task would be associated with a
> Closid at a time and this patch adds a new field closid to task_struct
> to keep track of the same.
> 
> Signed-off-by: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> ---
>  arch/x86/include/asm/intel_rdt.h | 12 ++++++
>  arch/x86/kernel/cpu/intel_rdt.c  | 82 +++++++++++++++++++++++++++++++++++++++-
>  include/linux/sched.h            |  3 ++
>  3 files changed, 95 insertions(+), 2 deletions(-)
>  create mode 100644 arch/x86/include/asm/intel_rdt.h
> 
> diff --git a/arch/x86/include/asm/intel_rdt.h b/arch/x86/include/asm/intel_rdt.h
> new file mode 100644
> index 0000000..88b7643
> --- /dev/null
> +++ b/arch/x86/include/asm/intel_rdt.h
> @@ -0,0 +1,12 @@
> +#ifndef _RDT_H_
> +#define _RDT_H_
> +
> +#ifdef CONFIG_INTEL_RDT
> +
> +struct clos_cbm_table {
> +	unsigned long l3_cbm;
> +	unsigned int clos_refcnt;
> +};

Isn't this a single entry?

> +
> +#endif
> +#endif
> diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
> index f49e970..d79213a 100644
> --- a/arch/x86/kernel/cpu/intel_rdt.c
> +++ b/arch/x86/kernel/cpu/intel_rdt.c
> @@ -24,17 +24,95 @@
>  
>  #include <linux/slab.h>
>  #include <linux/err.h>
> +#include <asm/intel_rdt.h>
> +
> +/*
> + * 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(rdt_group_mutex);
> +
> +static inline void closid_get(u32 closid)
> +{
> +	struct clos_cbm_table *cct = &cctable[closid];
> +
> +	lockdep_assert_held(&rdt_group_mutex);
> +
> +	cct->clos_refcnt++;
> +}
> +
> +static int closid_alloc(u32 *closid)
> +{
> +	u32 maxid;
> +	u32 id;
> +
> +	lockdep_assert_held(&rdt_group_mutex);
> +
> +	maxid = boot_cpu_data.x86_cache_max_closid;
> +	id = find_first_zero_bit(closmap, maxid);
> +	if (id == maxid)
> +		return -ENOSPC;

This causes echo to print "No space left in device" when you run
out of CBMs. I think -ENOMEM makes more sense.

> +
> +	set_bit(id, closmap);
> +	closid_get(id);
> +	*closid = id;
> +
> +	return 0;
> +}
> +
> +static inline void closid_free(u32 closid)
> +{
> +	clear_bit(closid, closmap);
> +	cctable[closid].l3_cbm = 0;
> +}
> +
> +static void closid_put(u32 closid)
> +{
> +	struct clos_cbm_table *cct = &cctable[closid];
> +
> +	lockdep_assert_held(&rdt_group_mutex);
> +	if (WARN_ON(!cct->clos_refcnt))
> +		return;
> +
> +	if (!--cct->clos_refcnt)
> +		closid_free(closid);
> +}

This is very minor, but IMHO you got closid_put() and closid_free()
naming backwards. closeid_free() is the opposite operation of
closeid_alloc(). Likewise, closeid_put() is the opposite of
closide_get().

>  
>  static int __init intel_rdt_late_init(void)
>  {
>  	struct cpuinfo_x86 *c = &boot_cpu_data;
> +	u32 maxid, max_cbm_len;
> +	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;
> +	max_cbm_len = c->x86_cache_max_cbm_len;
>  
> -	return 0;
> +	size = maxid * sizeof(struct clos_cbm_table);
> +	cctable = kzalloc(size, GFP_KERNEL);
> +	if (!cctable) {
> +		err = -ENOMEM;
> +		goto out_err;
> +	}
> +
> +	size = BITS_TO_LONGS(maxid) * sizeof(long);
> +	closmap = kzalloc(size, GFP_KERNEL);
> +	if (!closmap) {
> +		kfree(cctable);
> +		err = -ENOMEM;
> +		goto out_err;
> +	}
> +
> +	pr_info("Intel cache allocation enabled\n");
> +out_err:
> +
> +	return err;
>  }
>  
>  late_initcall(intel_rdt_late_init);
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b7b9501..24bfbac 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1668,6 +1668,9 @@ struct task_struct {
>  	/* cg_list protected by css_set_lock and tsk->alloc_lock */
>  	struct list_head cg_list;
>  #endif
> +#ifdef CONFIG_INTEL_RDT
> +	u32 closid;
> +#endif
>  #ifdef CONFIG_FUTEX
>  	struct robust_list_head __user *robust_list;
>  #ifdef CONFIG_COMPAT

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