linux-kernel - Re: [PATCH v2] x86/centaur: report correct CPU/cache topology

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Date:   Thu, 26 Apr 2018 11:11:59 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Wang <davidwang@...oxin.com>
cc:     mingo@...hat.com, hpa@...or.com, gregkh@...uxfoundation.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        brucechang@...-alliance.com, cooperyan@...oxin.com,
        qiyuanwang@...oxin.com, benjaminpan@...tech.com,
        lukelin@...cpu.com, timguo@...oxin.com
Subject: Re: [PATCH v2] x86/centaur: report correct CPU/cache topology

On Wed, 25 Apr 2018, David Wang wrote:
>  
> +static void early_init_centaur_mc(struct cpuinfo_x86 *c)
> +{
> +#ifdef CONFIG_SMP
> +	unsigned int eax, ebx, ecx, edx;
> +
> +	if (c->cpuid_level < 4)
> +		return;
> +
> +	cpuid_count(4, 0, &eax, &ebx, &ecx, &edx);
> +	if (eax & 0x1f)
> +		c->x86_max_cores = (eax >> 26) + 1;
> +	else
> +		return;
> +#endif
> +}

My review comment from last time still stands:

> > This is a bad copy of intel_num_cpu_cores(). See for the subtle
> > difference. Please rename the intel function and move it to common.c

In other words:

Make a patch which moves intel_num_cpu_cores() into common.c. Rename the
function into something like detect_num_cpu_cores() and fix up the call
site in intel.c.

Then add your patch and use the very same function.

> +
>  static void early_init_centaur(struct cpuinfo_x86 *c)
>  {
> +	early_init_centaur_mc(c);
>  	switch (c->x86) {
>  #ifdef CONFIG_X86_32
>  	case 5:
> @@ -146,6 +163,7 @@ static void centaur_detect_vmx_virtcap(struct cpuinfo_x86 *c)
>  
>  static void init_centaur(struct cpuinfo_x86 *c)
>  {
> +	unsigned int l2 = 0;
>  #ifdef CONFIG_X86_32
>  	char *name;
>  	u32  fcr_set = 0;
> @@ -161,6 +179,17 @@ static void init_centaur(struct cpuinfo_x86 *c)
>  #endif
>  	early_init_centaur(c);
>  
> +	l2 = init_intel_cacheinfo(c);
> +
> +	/* Detect legacy cache sizes if init_intel_cacheinfo did not */
> +	if (l2 == 0) {
> +		cpu_detect_cache_sizes(c);
> +	}

Aside of the pointless parentheses, this really wants to be cleaned up as
well.

init_intel_cacheinfo() is called from the intel init code and it does the
same silly thing.

So the right thing to do is in a separate patch first

--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -679,12 +679,6 @@ static void init_intel(struct cpuinfo_x8
 
 	l2 = init_intel_cacheinfo(c);
 
-	/* Detect legacy cache sizes if init_intel_cacheinfo did not */
-	if (l2 == 0) {
-		cpu_detect_cache_sizes(c);
-		l2 = c->x86_cache_size;
-	}
-
 	if (c->cpuid_level > 9) {
 		unsigned eax = cpuid_eax(10);
 		/* Check for version and the number of counters */
--- a/arch/x86/kernel/cpu/intel_cacheinfo.c
+++ b/arch/x86/kernel/cpu/intel_cacheinfo.c
@@ -802,6 +802,11 @@ unsigned int init_intel_cacheinfo(struct
 
 	c->x86_cache_size = l3 ? l3 : (l2 ? l2 : (l1i+l1d));
 
+	/* Detect legacy cache sizes if the above did not work */
+	if (!l2) {
+		cpu_detect_cache_sizes(c);
+		l2 = c->x86_cache_size;
+	}
 	return l2;
 }
 
Hmm?

	tglx