Fixed error when libcpuid reports zero number of CPU cores [#METR-219…

…26].

dbms/include/DB/Common/getNumberOfPhysicalCPUCores.h

@@ -1,4 +1,4 @@
 #pragma once
 
-/// Получить количество ядер CPU без учёта hyper-threading.
+/// Get number of CPU cores without hyper-threading.
 unsigned getNumberOfPhysicalCPUCores();

dbms/src/Common/getNumberOfPhysicalCPUCores.cpp

@@ -1,4 +1,5 @@
 #include <DB/Common/getNumberOfPhysicalCPUCores.h>
+#include <thread>
 
 #if defined(__x86_64__)
 
@@ -7,10 +8,6 @@
 
 	namespace DB { namespace ErrorCodes { extern const int CPUID_ERROR; }}
 
-#elif defined(__aarch64__)
-
-	#include <thread>
-
 #endif
 
 
@@ -26,10 +23,14 @@ unsigned getNumberOfPhysicalCPUCores()
 	if (0 != cpu_identify(&raw_data, &data))
 		throw DB::Exception("Cannot cpu_identify: " + std::string(cpuid_error()), DB::ErrorCodes::CPUID_ERROR);
 
+	/// On Xen VMs, libcpuid returns wrong info (zero number of cores). Fallback to alternative method.
+	if (data.num_cores == 0 || data.total_logical_cpus == 0 || data.num_logical_cpus == 0)
+		return std::thread::hardware_concurrency();
+
 	return data.num_cores * data.total_logical_cpus / data.num_logical_cpus;
 
 #elif defined(__aarch64__)
-	/// Считаем, что на этой системе нет hyper-threading.
+	/// Assuming there are no hyper-threading on the system.
 	return std::thread::hardware_concurrency();
 #endif
 }