Prefer MMIO interface in AUTO selection on Linux (ERDT+MRRM sysfs detection)

Presence of the tables ERDT and MRRM shows that MMIO interace is
supported. Choose it by default.

Signed-off-by: Roman Storozhenko <roman.storozhenko@intel.com>

Author: rstorozh

lib/acpi.c

@@ -50,9 +50,8 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#define DEV_MEM            "/dev/mem"
-#define EFI_SYSTAB         "/sys/firmware/efi/systab"
-#define ACPI_TABLE_FS_PATH "/sys/firmware/acpi/tables"
+#define DEV_MEM    "/dev/mem"
+#define EFI_SYSTAB "/sys/firmware/efi/systab"
 
 #define BIOS_RO_MEM_ADDR 0x000E0000LLU
 #define BIOS_RO_MEM_SIZE 0x00020000LLU

lib/acpi.h

@@ -57,6 +57,9 @@ typedef uint32_t acpi_size;
 #error "Unsupported architecture"
 #endif
 
+/* ACPI tables root directory in sysfs */
+#define ACPI_TABLE_FS_PATH "/sys/firmware/acpi/tables"
+
 /**
  * ACPI Table
  */

lib/cap.c

@@ -50,8 +50,10 @@
 
 #include "cap.h"
 
+#include "acpi.h"
 #include "allocation.h"
 #include "api.h"
+#include "common.h"
 #include "cores_domains.h"
 #include "cpu_registers.h"
 #include "cpuinfo.h"
@@ -71,6 +73,9 @@
 
 #include <stdlib.h>
 #include <string.h>
+#ifdef __linux__
+#include <unistd.h>
+#endif
 
 /**
  * ---------------------------------------
@@ -80,6 +85,11 @@
 
 #define PROC_CPUINFO "/proc/cpuinfo"
 
+#ifdef __linux__
+#define ACPI_ERDT_TABLE (ACPI_TABLE_FS_PATH "/" ACPI_TABLE_SIG_ERDT)
+#define ACPI_MRRM_TABLE (ACPI_TABLE_FS_PATH "/" ACPI_TABLE_SIG_MRRM)
+#endif
+
 /**
  * ---------------------------------------
  * Local data types
@@ -618,6 +628,26 @@ _cap_interface_to_string(enum pqos_interface interface)
         }
 }
 
+#ifdef __linux__
+/**
+ * @brief Checks if MMIO interface prerequisites are present via Linux sysfs
+ *
+ * MMIO interface requires both ERDT and MRRM ACPI tables.
+ * This mirrors the requirement already enforced in pqos_init() for MMIO.
+ *
+ * @return 1 if MMIO is supported, 0 otherwise
+ */
+PQOS_STATIC int
+mmio_is_supported_sysfs(void)
+{
+        if (!pqos_file_exists(ACPI_ERDT_TABLE) ||
+            !pqos_file_exists(ACPI_MRRM_TABLE))
+                return 0;
+
+        return 1;
+}
+#endif
+
 /**
  * @brief Detects interface
  *
@@ -689,7 +719,10 @@ discover_interface(enum pqos_interface requested_interface,
                 }
         } else if (requested_interface == PQOS_INTER_AUTO) {
 #ifdef __linux__
-                if (resctrl_is_supported() == PQOS_RETVAL_OK)
+                /* Prefer MMIO if platform supports it */
+                if (mmio_is_supported_sysfs())
+                        *interface = PQOS_INTER_MMIO;
+                else if (resctrl_is_supported() == PQOS_RETVAL_OK)
                         *interface = PQOS_INTER_OS;
                 else
                         *interface = PQOS_INTER_MSR;
@@ -700,8 +733,8 @@ discover_interface(enum pqos_interface requested_interface,
                 *interface = requested_interface;
         }
 
-        LOG_INFO("Selected interface: %s\n",
-                 _cap_interface_to_string(*interface));
+        fprintf(stdout, "Selected interface: %s\n",
+                _cap_interface_to_string(*interface));
         return PQOS_RETVAL_OK;
 }
 

pqos/main.c

@@ -1171,9 +1171,11 @@ static const char help_printf_long[] =
     "          If automatic detection is selected ('auto'), it:\n"
     "                  1) Takes RDT_IFACE environment variable\n"
     "                     into account if this variable is set\n"
-    "                  2) Selects OS interface if the kernel interface\n"
+    "                  2) Selects MMIO interface if supported\n"
+    "                     (ERDT and MRRM ACPI tables present)\n"
+    "                  3) Selects OS interface if the kernel interface\n"
     "                     is supported\n"
-    "                  3) Selects MSR interface otherwise\n\n"
+    "                  4) Selects MSR interface otherwise\n\n"
     "---------------- MMIO interface help section ----------------\n"
     "-------------------  Detect capabilities --------------------\n"
     "  --print-mem-regions         print memory mapped regions\n"

pqos/pqos.8

@@ -333,9 +333,11 @@ INTERFACE can be set to either 'auto' (default), 'msr' or 'os'. If automatic det
 .br
 1) Takes RDT_IFACE environment variable into account if this variable is set
 .br
-2) Selects OS interface if the kernel interface is supported
+2) Selects MMIO interface if supported (ERDT and MRRM ACPI tables present)
 .br
-3) Selects MSR interface otherwise
+3) Selects OS interface if the kernel interface is supported
+.br
+4) Selects MSR interface otherwise
 .SH NOTES
 .PP
 CMT, MBM and CAT are configured using Model Specific Registers (MSRs). The pqos software

unit-test/lib/Makefile

@@ -758,6 +758,7 @@ $(BIN_DIR)/test_cap_static: ./test_cap_static.c $(LIB_OBJS)
 	mkdir -p $(BIN_DIR)
 	$(CC) $(CFLAGS) $(WRAP) \
 		-Wl,--wrap=getenv \
+		-Wl,--wrap=access \
 		-Wl,--wrap=malloc \
 		-Wl,--wrap=hw_cap_l3ca_discover \
 		-Wl,--wrap=os_cap_l3ca_discover \

unit-test/lib/test_cap_static.c

@@ -35,6 +35,9 @@
 #include "pqos.h"
 #include "test.h"
 #include "test_cap.h"
+#ifdef __linux__
+#include <unistd.h>
+#endif
 
 /* ======== helpers ======= */
 
@@ -110,6 +113,17 @@ __wrap_getenv(const char *name)
         return mock_ptr_type(char *);
 }
 
+#ifdef __linux__
+int
+__wrap_access(const char *pathname, int mode)
+{
+        function_called();
+        check_expected_ptr(pathname);
+        check_expected(mode);
+        return mock_type(int);
+}
+#endif
+
 static int log_init_result = LOG_RETVAL_OK;
 int
 __wrap_log_init(int fd_log __attribute__((unused)),
@@ -534,18 +548,68 @@ test_discover_interface_auto_linux(void **state __attribute__((unused)))
 
         disable_check_log_printf();
 
+        /* MMIO supported (both ERDT and MRRM present) -> select MMIO */
+        interface = -1;
+        expect_function_call(__wrap_getenv);
+        will_return(__wrap_getenv, NULL);
+        expect_function_call(__wrap_access);
+        expect_string(__wrap_access, pathname,
+                      "/sys/firmware/acpi/tables/ERDT");
+        expect_value(__wrap_access, mode, F_OK);
+        will_return(__wrap_access, 0);
+        expect_function_call(__wrap_access);
+        expect_string(__wrap_access, pathname,
+                      "/sys/firmware/acpi/tables/MRRM");
+        expect_value(__wrap_access, mode, F_OK);
+        will_return(__wrap_access, 0);
+        ret = discover_interface(PQOS_INTER_AUTO, &interface);
+        assert_int_equal(ret, PQOS_RETVAL_OK);
+        assert_int_equal(interface, PQOS_INTER_MMIO);
+
+        /* ERDT missing -> fall through to OS if resctrl supported */
+        interface = -1;
+        expect_function_call(__wrap_getenv);
+        will_return(__wrap_getenv, NULL);
+        expect_function_call(__wrap_access);
+        expect_string(__wrap_access, pathname,
+                      "/sys/firmware/acpi/tables/ERDT");
+        expect_value(__wrap_access, mode, F_OK);
+        will_return(__wrap_access, -1);
+        expect_function_call(__wrap_resctrl_is_supported);
+        will_return(__wrap_resctrl_is_supported, PQOS_RETVAL_OK);
+        ret = discover_interface(PQOS_INTER_AUTO, &interface);
+        assert_int_equal(ret, PQOS_RETVAL_OK);
+        assert_int_equal(interface, PQOS_INTER_OS);
+
+        /* ERDT present but MRRM missing -> fall through to OS if resctrl */
         interface = -1;
         expect_function_call(__wrap_getenv);
         will_return(__wrap_getenv, NULL);
+        expect_function_call(__wrap_access);
+        expect_string(__wrap_access, pathname,
+                      "/sys/firmware/acpi/tables/ERDT");
+        expect_value(__wrap_access, mode, F_OK);
+        will_return(__wrap_access, 0);
+        expect_function_call(__wrap_access);
+        expect_string(__wrap_access, pathname,
+                      "/sys/firmware/acpi/tables/MRRM");
+        expect_value(__wrap_access, mode, F_OK);
+        will_return(__wrap_access, -1);
         expect_function_call(__wrap_resctrl_is_supported);
         will_return(__wrap_resctrl_is_supported, PQOS_RETVAL_OK);
         ret = discover_interface(PQOS_INTER_AUTO, &interface);
         assert_int_equal(ret, PQOS_RETVAL_OK);
         assert_int_equal(interface, PQOS_INTER_OS);
 
+        /* MMIO not supported, resctrl not supported -> select MSR */
         interface = -1;
         expect_function_call(__wrap_getenv);
         will_return(__wrap_getenv, NULL);
+        expect_function_call(__wrap_access);
+        expect_string(__wrap_access, pathname,
+                      "/sys/firmware/acpi/tables/ERDT");
+        expect_value(__wrap_access, mode, F_OK);
+        will_return(__wrap_access, -1);
         expect_function_call(__wrap_resctrl_is_supported);
         will_return(__wrap_resctrl_is_supported, PQOS_RETVAL_ERROR);
         ret = discover_interface(PQOS_INTER_AUTO, &interface);