[PATCH] When L3 is present show its size in /proc/cpuinfo

[PATCH] When L3 is present show its size in /proc/cpuinfo

[Venkatesh Pallipadi]

The code that prints the cache size assumes that L3 always lives in chipset and
is shared across CPUs. Which is not really true.

I think all the cachesizes reported by cpuid are in the processor itself. The
attached patch changes the code to reflect that.

Dave, any idea where that original comment in the code came from? Are there any
systems which reports the L3 cache size in cpuid, when L3 sits in northbridge?

Thanks,
Venki

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>

Index: linux-2.6.12/arch/i386/kernel/cpu/intel_cacheinfo.c
===================================================================
--- linux-2.6.12.orig/arch/i386/kernel/cpu/intel_cacheinfo.c	2005-08-31 14:46:40.474386680 -0700
+++ linux-2.6.12/arch/i386/kernel/cpu/intel_cacheinfo.c	2005-09-12 11:47:06.639700640 -0700
@@ -284,13 +284,7 @@
 		if ( l3 )
 			printk(KERN_INFO "CPU: L3 cache: %dK\n", l3);
 
-		/*
-		 * This assumes the L3 cache is shared; it typically lives in
-		 * the northbridge.  The L1 caches are included by the L2
-		 * cache, and so should not be included for the purpose of
-		 * SMP switching weights.
-		 */
-		c->x86_cache_size = l2 ? l2 : (l1i+l1d);
+		c->x86_cache_size = l3 ? l3 : (l2 ? l2 : (l1i+l1d));
 	}
 
 	return l2;

Re: [PATCH] When L3 is present show its size in /proc/cpuinfo

[Dave Jones]

On Mon, Sep 26, 2005 at 02:59:56PM -0700, Venkatesh Pallipadi wrote:
 
 > The code that prints the cache size assumes that L3 always lives in chipset and
 > is shared across CPUs. Which is not really true.
 > 
 > I think all the cachesizes reported by cpuid are in the processor itself.
 > The attached patch changes the code to reflect that.
 > 
 > Dave, any idea where that original comment in the code came from?

Been there for a long time iirc (Though I've not checked [my kingdom for
a 'git annotate' tool])

 > Are there any
 > systems which reports the L3 cache size in cpuid, when L3 sits in northbridge?

Very unlikely.
The only legacy system with L3 that I recall was the AMD K6-III (which had on-CPU L1/L2,
though some motherboards at the time also included an L3 (or L2 if used with an earlier
socket 7 cpu).  None of those off-cpu caches were detectable with cpuid, and
required reading from pci config space to determine their size/status etc.

The big question I have though is how relevant that 'weighting' is today
if we factor in L3.

		Dave