linux-kernel - Re: [PATCH v6 09/24] x86/resctrl: Use set_bit()/clear

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Date:   Tue, 3 Oct 2023 14:14:23 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Fenghua Yu <fenghua.yu@...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>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        <carl@...amperecomputing.com>, <lcherian@...vell.com>,
        <bobo.shaobowang@...wei.com>, <tan.shaopeng@...itsu.com>,
        <xingxin.hx@...nanolis.org>, <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 v6 09/24] x86/resctrl: Use set_bit()/clear_bit() instead
 of open coding

Hi James,

On 9/14/2023 10:21 AM, 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 resctrl_closid_is_free(), which adds more open

resctrl_closid_is_free() is not added in this series.

> 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.
> 
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Tested-By: Peter Newman <peternewman@...gle.com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index ac1a6437469f..fa449ee0d1a7 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -106,7 +106,7 @@ 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)
> @@ -126,7 +126,7 @@ 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(0, &closid_free_map);
>  	closid_free_map_len = rdt_min_closid;
>  }
>  
> @@ -137,14 +137,14 @@ static int closid_alloc(void)
>  	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;
> +	set_bit(closid, &closid_free_map);
>  }
>  
>  /**
> @@ -156,7 +156,7 @@ void closid_free(int closid)
>   */
>  static bool closid_allocated(unsigned int closid)
>  {
> -	return (closid_free_map & (1 << closid)) == 0;
> +	return !test_bit(closid, &closid_free_map);
>  }
>  
>  /**

The patch looks good to me.

Reinette