linux-kernel - Re: [PATCH v7 09/24] x86/resctrl: Use __set_bit()/__clear

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Message-ID: <c87a34c6-7163-4025-9f5a-4b9225701b66@amd.com>
Date:   Thu, 9 Nov 2023 14:38:42 -0600
From:   "Moger, Babu" <babu.moger@....com>
To:     James Morse <james.morse@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <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>,
        shameerali.kolothum.thodi@...wei.com,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
        dfustini@...libre.com, amitsinght@...vell.com
Subject: Re: [PATCH v7 09/24] x86/resctrl: Use __set_bit()/__clear_bit()
 instead of open coding

Hi James,

On 10/25/23 13:03, James Morse wrote:
> The resctrl CLOSID allocator uses a single 32bit word to track which
> CLOSID are free. The setting and clearing of bits is open coded.
> 
> A subsequent patch adds closid_allocated(), which adds more open
> coded bitmaps operations. These will eventually need changing to use
> the bitops helpers so that a CLOSID bitmap of the correct size can be
> allocated dynamically.
> 
> Convert the existing open coded bit manipulations of closid_free_map
> to use __set_bit() and friends. These don't need to be atomic as this
> list is protected by the mutex.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>

Reviewed-by: Babu Moger <babu.moger@....com>

> 
> ---
> Changes since v6:
>  * Use the __ inatomic helpers and add lockdep_assert_held() annotations to
>    document how this is safe.
>  * Fixed a resctrl_closid_is_free()/closid_allocated() rename in the commit
>    message.
>  * Use RESCTRL_RESERVED_CLOSID to improve readability.
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 9864cb49d58c..f6051a3e7262 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
>   * - 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)
> @@ -131,7 +131,7 @@ static void closid_init(void)
>  	closid_free_map = BIT_MASK(rdt_min_closid) - 1;
>  
>  	/* CLOSID 0 is always reserved for the default group */
> -	closid_free_map &= ~1;
> +	__clear_bit(RESCTRL_RESERVED_CLOSID, &closid_free_map);
>  	closid_free_map_len = rdt_min_closid;
>  }
>  
> @@ -139,17 +139,21 @@ static int closid_alloc(void)
>  {
>  	u32 closid = ffs(closid_free_map);
>  
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
>  	if (closid == 0)
>  		return -ENOSPC;
>  	closid--;
> -	closid_free_map &= ~(1 << closid);
> +	__clear_bit(closid, &closid_free_map);
>  
>  	return closid;
>  }
>  
>  void closid_free(int closid)
>  {
> -	closid_free_map |= 1 << closid;
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	__set_bit(closid, &closid_free_map);
>  }
>  
>  /**
> @@ -161,7 +165,9 @@ void closid_free(int closid)
>   */
>  static bool closid_allocated(unsigned int closid)
>  {
> -	return (closid_free_map & (1 << closid)) == 0;
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	return !test_bit(closid, &closid_free_map);
>  }
>  
>  /**

-- 
Thanks
Babu Moger