linux-kernel - Re: [PATCH V2 04/10] x86/resctrl: Set cache line size using new utility

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Date:   Mon, 5 Aug 2019 17:57:39 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     tglx@...utronix.de, fenghua.yu@...el.com, tony.luck@...el.com,
        kuo-lang.tseng@...el.com, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 04/10] x86/resctrl: Set cache line size using new
 utility

On Tue, Jul 30, 2019 at 10:29:38AM -0700, Reinette Chatre wrote:
> In preparation for support of pseudo-locked regions spanning two
> cache levels the cache line size computation is moved to a utility.

Please write this in active voice: "Move the cache line size computation
to a utility function in preparation... "

And yes, "a utility" solely sounds like you're adding a tool which does
that. But it is simply a separate function. :-)

> Setting of the cache line size is moved a few lines earlier, before
> the C-states are constrained, to reduce the amount of cleanup needed
> on failure.

And in general, that passive voice is kinda hard to read. To quote from
Documentation/process/submitting-patches.rst:

 "Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
  instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
  to do frotz", as if you are giving orders to the codebase to change
  its behaviour."

Please check all your commit messages.

> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> ---
>  arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 42 +++++++++++++++++------
>  1 file changed, 31 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index 110ae4b4f2e4..884976913326 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -101,6 +101,30 @@ static u64 get_prefetch_disable_bits(void)
>  	return 0;
>  }
>  
> +/**
> + * get_cache_line_size - Determine the cache coherency line size
> + * @cpu: CPU with which cache is associated
> + * @level: Cache level
> + *
> + * Context: @cpu has to be online.
> + * Return: The cache coherency line size for cache level @level associated
> + * with CPU @cpu. Zero on failure.
> + */
> +static unsigned int get_cache_line_size(unsigned int cpu, int level)
> +{
> +	struct cpu_cacheinfo *ci;
> +	int i;
> +
> +	ci = get_cpu_cacheinfo(cpu);
> +
> +	for (i = 0; i < ci->num_leaves; i++) {
> +		if (ci->info_list[i].level == level)
> +			return ci->info_list[i].coherency_line_size;
> +	}
> +
> +	return 0;
> +}
> +
>  /**
>   * pseudo_lock_minor_get - Obtain available minor number
>   * @minor: Pointer to where new minor number will be stored
> @@ -281,9 +305,7 @@ static void pseudo_lock_region_clear(struct pseudo_lock_region *plr)
>   */
>  static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>  {
> -	struct cpu_cacheinfo *ci;
>  	int ret;
> -	int i;
>  
>  	/* Pick the first cpu we find that is associated with the cache. */
>  	plr->cpu = cpumask_first(&plr->d->cpu_mask);
> @@ -295,7 +317,12 @@ static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>  		goto out_region;
>  	}
>  
> -	ci = get_cpu_cacheinfo(plr->cpu);
> +	plr->line_size = get_cache_line_size(plr->cpu, plr->r->cache_level);
> +	if (plr->line_size == 0) {

	if (!plr->...)

> +		rdt_last_cmd_puts("Unable to determine cache line size\n");
> +		ret = -1;
> +		goto out_region;
> +	}
>  
>  	plr->size = rdtgroup_cbm_to_size(plr->r, plr->d, plr->cbm);
>  
> @@ -303,15 +330,8 @@ static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>  	if (ret < 0)
>  		goto out_region;
>  
> -	for (i = 0; i < ci->num_leaves; i++) {
> -		if (ci->info_list[i].level == plr->r->cache_level) {
> -			plr->line_size = ci->info_list[i].coherency_line_size;
> -			return 0;
> -		}
> -	}
> +	return 0;
>  
> -	ret = -1;
> -	rdt_last_cmd_puts("Unable to determine cache line size\n");
>  out_region:
>  	pseudo_lock_region_clear(plr);
>  	return ret;
> -- 
> 2.17.2
> 

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.