Re: [PATCH v5 08/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid

[Fenghua Yu <fenghua.yu@intel.com>]

Hi, James,

On 7/28/23 09:42, James Morse wrote:
> MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
> used for different control groups.
> 
> This means once a CLOSID is allocated, all its monitoring ids may still be
> dirty, and held in limbo.
> 
> Instead of allocating the first free CLOSID, on architectures where
> CONFIG_RESCTRL_RMID_DEPENDS_ON_COSID is enabled, search
> closid_num_dirty_rmid[] to find the cleanest CLOSID.
> 
> The CLOSID found is returned to closid_alloc() for the free list
> to be updated.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v4:
>   * Dropped stale section from comment
> ---
>   arch/x86/kernel/cpu/resctrl/internal.h |  2 ++
>   arch/x86/kernel/cpu/resctrl/monitor.c  | 42 ++++++++++++++++++++++++++
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++---
>   3 files changed, 58 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 94749ee950dd..7c2a1c235480 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -557,5 +557,7 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
>   void __init thread_throttle_mode_init(void);
>   void __init mbm_config_rftype_init(const char *config);
>   void rdt_staged_configs_clear(void);
> +bool closid_allocated(unsigned int closid);
> +int resctrl_find_cleanest_closid(void);
>   
>   #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 44addc0126fc..c268aa5925c7 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -379,6 +379,48 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
>   	return ERR_PTR(-ENOSPC);
>   }
>   
> +/**
> + * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
> + *                                  RMID are clean, or the CLOSID that has
> + *                                  the most clean RMID.
> + *
> + * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
> + * may not be able to allocate clean RMID. To avoid this the allocator will
> + * choose the CLOSID with the most clean RMID.
> + *
> + * When the CLOSID and RMID are independent numbers, the first free CLOSID will
> + * be returned.
> + */
> +int resctrl_find_cleanest_closid(void)
> +{
> +	u32 cleanest_closid = ~0, iter_num_dirty;
> +	int i = 0;
> +
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
> +		return -EIO;
> +
> +	for (i = 0; i < closids_supported(); i++) {
> +		if (closid_allocated(i))
> +			continue;
> +
> +		iter_num_dirty = closid_num_dirty_rmid[i];
> +		if (iter_num_dirty == 0)
> +			return i;
> +
> +		if (cleanest_closid == ~0)
> +			cleanest_closid = i;
> +
> +		if (iter_num_dirty < closid_num_dirty_rmid[cleanest_closid])
> +			cleanest_closid = i;
> +	}
> +
> +	if (cleanest_closid == ~0)
> +		return -ENOSPC;
> +	return cleanest_closid;
> +}
> +

resctrl_find_cleanest_closid() is not empty on x86 after compiled 
although it's very short. After all, the function is irrelevant to x86 
and could be completely empty on x86.

If put the function in
#ifdef CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID
resctrl_find_cleanest_closid()
...
#else
resctrl_find_cleanest_closid() {}
#endif

It's fully empty on x86.

>   /*
>    * For MPAM the RMID value is not unique, and has to be considered with
>    * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 4ab9bb018c17..df28b81d2c9c 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -132,11 +132,20 @@ static void closid_init(void)
>   
>   static int closid_alloc(void)
>   {
> -	u32 closid = ffs(closid_free_map);
> +	u32 closid;
> +	int err;
>   
> -	if (closid == 0)
> -		return -ENOSPC;
> -	closid--;
> +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
> +		err = resctrl_find_cleanest_closid();
> +		if (err < 0)
> +			return err;
> +		closid = err;
> +	} else {
> +		closid = ffs(closid_free_map);
> +		if (closid == 0)
> +			return -ENOSPC;
> +		closid--;
> +	}
>   	clear_bit(closid, &closid_free_map);
>   
>   	return closid;
> @@ -154,7 +163,7 @@ void closid_free(int closid)
>    * Return: true if @closid is currently associated with a resource group,
>    * false if @closid is free
>    */
> -static bool closid_allocated(unsigned int closid)
> +bool closid_allocated(unsigned int closid)
>   {
>   	return !test_bit(closid, &closid_free_map);
>   }

Thanks.

-Fenghua