[COMMITTED 2.31] x86: Optimizing memcpy for AMD Zen architecture.

[COMMITTED 2.31] x86: Optimizing memcpy for AMD Zen architecture.

[Florian Weimer]

From: Sajan Karumanchi <sajan.karumanchi@amd.com>

Modifying the shareable cache '__x86_shared_cache_size', which is a
factor in computing the non-temporal threshold parameter
'__x86_shared_non_temporal_threshold' to optimize memcpy for AMD Zen
architectures.
In the existing implementation, the shareable cache is computed as 'L3
per thread, L2 per core'. Recomputing this shareable cache as 'L3 per
CCX(Core-Complex)' has brought in performance gains.
As per the large bench variant results, this patch also addresses the
regression problem on AMD Zen architectures.

Backport of commit 59803e81f96b479c17f583b31eac44b57591a1bf upstream,
with the fix from cb3a749a22a55645dc6a52659eea765300623f98 ("x86:
Restore processing of cache size tunables in init_cacheinfo") applied.

Reviewed-by: Premachandra Mallappa <premachandra.mallappa@amd.com>
Co-Authored-by: Florian Weimer <fweimer@redhat.com>

---
 sysdeps/x86/cacheinfo.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c
index 43f2e7445c..39c13b7195 100644
--- a/sysdeps/x86/cacheinfo.c
+++ b/sysdeps/x86/cacheinfo.c
@@ -722,7 +722,7 @@ intel_bug_no_cache_info:
 	      threads = 1 << ((ecx >> 12) & 0x0f);
 	    }
 
-	  if (threads == 0)
+	  if (threads == 0 || cpu_features->basic.family >= 0x17)
 	    {
 	      /* If APIC ID width is not available, use logical
 		 processor count.  */
@@ -737,8 +737,22 @@ intel_bug_no_cache_info:
 	  if (threads > 0)
 	    shared /= threads;
 
-	  /* Account for exclusive L2 and L3 caches.  */
-	  shared += core;
+	  /* Get shared cache per ccx for Zen architectures.  */
+	  if (cpu_features->basic.family >= 0x17)
+	    {
+	      unsigned int eax;
+
+	      /* Get number of threads share the L3 cache in CCX.  */
+	      __cpuid_count (0x8000001D, 0x3, eax, ebx, ecx, edx);
+
+	      unsigned int threads_per_ccx = ((eax >> 14) & 0xfff) + 1;
+	      shared *= threads_per_ccx;
+	    }
+	  else
+	    {
+	      /* Account for exclusive L2 and L3 caches.  */
+	      shared += core;
+            }
 	}
 
 #ifndef DISABLE_PREFETCHW

-- 
Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill