linux-kernel - [Patch v2 2/2] amd: uncore: Get correct number of cores sharing last level cache

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Message-Id: <358964e78b06c24422da14a1311119eb8ae06580.1496950330.git.Janakarajan.Natarajan@amd.com>
Date:   Thu,  8 Jun 2017 14:48:24 -0500
From:   Janakarajan Natarajan <Janakarajan.Natarajan@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>
Subject: [Patch v2 2/2] amd: uncore: Get correct number of cores sharing last level cache

In Family 17h, the number of cores sharing a cache level is obtained
from the Cache Properties CPUID leaf (0x8000001d) by passing in the
cache level in ECX. In prior families, a cache level of 2 was used to
determine this information.

To get the right information, irrespective of Family, iterate over
the cache levels using CPUID 0x8000001d. The last level cache is the
last value to return a non-zero value in EAX.

Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@....com>
---
 arch/x86/events/amd/uncore.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index e34f8a6..6952262 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -400,11 +400,22 @@ static int amd_uncore_cpu_starting(unsigned int cpu)
 
 	if (amd_uncore_llc) {
 		unsigned int apicid = cpu_data(cpu).apicid;
-		unsigned int nshared;
+		unsigned int nshared, cache_topology, prev_eax = 0;
 
 		uncore = *per_cpu_ptr(amd_uncore_llc, cpu);
-		cpuid_count(0x8000001d, 2, &eax, &ebx, &ecx, &edx);
-		nshared = ((eax >> 14) & 0xfff) + 1;
+		/*
+		 * Iterate over Cache Topology Definition leaves until no
+		 * more cache descriptions are available
+		 */
+		for(cache_topology = 0; cache_topology < 5; cache_topology++) {
+			cpuid_count(0x8000001d, cache_topology, &eax, &ebx, &ecx, &edx);
+
+			if ((eax & 0x1f) == 0) /* EAX[0:4] gives type of cache */
+				break;
+
+			prev_eax = eax;
+		}
+		nshared = ((prev_eax >> 14) & 0xfff) + 1;
 		uncore->id = apicid - (apicid % nshared);
 
 		uncore = amd_uncore_find_online_sibling(uncore, amd_uncore_llc);
-- 
2.7.4