linux-kernel - RE: [PATCH v2 06/18] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID

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Message-ID: <IA1PR11MB609729461B9FF9F9BFD1DEC99BC69@IA1PR11MB6097.namprd11.prod.outlook.com>
Date:   Tue, 17 Jan 2023 18:29:01 +0000
From:   "Yu, Fenghua" <fenghua.yu@...el.com>
To:     James Morse <james.morse@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Chatre, Reinette" <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        "carl@...amperecomputing.com" <carl@...amperecomputing.com>,
        "lcherian@...vell.com" <lcherian@...vell.com>,
        "bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
        "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
        "xingxin.hx@...nanolis.org" <xingxin.hx@...nanolis.org>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>,
        "peternewman@...gle.com" <peternewman@...gle.com>
Subject: RE: [PATCH v2 06/18] x86/resctrl: Allow the allocator to check if a
 CLOSID can allocate clean RMID

Hi, James,

> 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.
> 
> Add a helper to allow the CLOSID allocator to check if a CLOSID has dirty RMID
> values. This behaviour is enabled by a kconfig option selected by the
> architecture, which avoids a pointless search for x86.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
> 
> ---
> Changes since v1:
>  * Removed superflous IS_ENABLED().
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h |  1 +
> arch/x86/kernel/cpu/resctrl/monitor.c  | 31 ++++++++++++++++++++++++++
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 17 ++++++++------
>  3 files changed, 42 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index 013c8fc9fd28..adae6231324f 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -509,6 +509,7 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup
> *rdtgrp);  void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp);  struct
> rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);  int
> closids_supported(void);
> +bool resctrl_closid_is_dirty(u32 closid);
>  void closid_free(int closid);
>  int alloc_rmid(u32 closid);
>  void free_rmid(u32 closid, u32 rmid);
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 347be3767241..190ac183139e 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -327,6 +327,37 @@ static struct rmid_entry *resctrl_find_free_rmid(u32
> closid)
>  	return ERR_PTR(-ENOSPC);
>  }
> 
> +/**
> + * resctrl_closid_is_dirty - Determine if clean RMID can be allocate for this

s/allocate/allocated/

> + *                           CLOSID.
> + * @closid: The CLOSID that is being queried.
> + *
> + * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocate

s/allocate/allocated/

> +CLOSID
> + * may not be able to allocate clean RMID. To avoid this the allocator
> +will
> + * only return clean CLOSID.
> + */
> +bool resctrl_closid_is_dirty(u32 closid) {
> +	struct rmid_entry *entry;
> +	int i;
> +
> +	lockdep_assert_held(&rdtgroup_mutex);

It's better to move lockdep_asser_held() after if (!IS_ENABLE()).
Then compiler might optimize this function to empty on X86.

> +
> +	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
> +		return false;
> +
> +	for (i = 0; i < resctrl_arch_system_num_rmid_idx(); i++) {
> +		entry = &rmid_ptrs[i];
> +		if (entry->closid != closid)
> +			continue;
> +
> +		if (entry->busy)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  /*
>   * As of now the RMIDs allocation is the same in each domain.
>   * However we keep track of which packages the RMIDs diff --git
> a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index ac88610a6946..e1f879e13823 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -93,7 +93,7 @@ void rdt_last_cmd_printf(const char *fmt, ...)
>   * - Our choices on how to configure each resource become progressively more
>   *   limited as the number of resources grows.
>   */
> -static int closid_free_map;
> +static unsigned long closid_free_map;
>  static int closid_free_map_len;
> 
>  int closids_supported(void)
> @@ -119,14 +119,17 @@ static void closid_init(void)
> 
>  static int closid_alloc(void)
>  {
> -	u32 closid = ffs(closid_free_map);
> +	u32 closid;
> 
> -	if (closid == 0)
> -		return -ENOSPC;
> -	closid--;
> -	closid_free_map &= ~(1 << closid);
> +	for_each_set_bit(closid, &closid_free_map, closid_free_map_len) {
> +		if (resctrl_closid_is_dirty(closid))
> +			continue;
> 
> -	return closid;
> +		clear_bit(closid, &closid_free_map);
> +		return closid;
> +	}
> +
> +	return -ENOSPC;
>  }
> 
>  void closid_free(int closid)
> --
> 2.30.2

Thanks.

-Fenghua