[ovs-dev] [PATCH v6 14/15] dpdk: Cache result of CPU ISA checks

[Harry van Haaren]

As a small optimization, this patch caches the result of a CPU ISA
check from DPDK. Particularly in the case of running the DPCLS
autovalidator (which repeatedly probes subtables) this reduces
the amount of CPU ISA lookups from the DPDK level.

By caching them at the OVS/dpdk.c level, the ISA checks remain
runtime for the CPU where they are executed, but subsequent checks
for the same ISA feature become much cheaper.

Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
Co-authored-by: Cian Ferriter <cian.ferriter at intel.com>
Signed-off-by: Cian Ferriter <cian.ferriter at intel.com>
---
 lib/dpdk.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/lib/dpdk.c b/lib/dpdk.c
index 319540394..703602603 100644
--- a/lib/dpdk.c
+++ b/lib/dpdk.c
@@ -614,13 +614,31 @@ print_dpdk_version(void)
     puts(rte_version());
 }
 
+/* Avoid calling rte_cpu_get_flag_enabled() excessively, by caching the
+ * result of the call for each CPU flag in a static variable. To avoid
+ * allocating large numbers of static variables, use a uint8 as a bitfield.
+ * Note the macro must only return if the ISA check is done and available.
+ */
+#define ISA_CHECK_DONE_BIT (1 << 0)
+#define ISA_AVAILABLE_BIT  (1 << 1)
+
 #define CHECK_CPU_FEATURE(feature, name_str, RTE_CPUFLAG)               \
     do {                                                                \
         if (strncmp(feature, name_str, strlen(name_str)) == 0) {        \
-            int has_isa = rte_cpu_get_flag_enabled(RTE_CPUFLAG);        \
-            VLOG_DBG("CPU flag %s, available %s\n", name_str,           \
-                      has_isa ? "yes" : "no");                          \
-            return true;                                                \
+            static uint8_t isa_check_##RTE_CPUFLAG;                     \
+            int check = isa_check_##RTE_CPUFLAG & ISA_CHECK_DONE_BIT;   \
+            if (OVS_UNLIKELY(!check)) {                                 \
+                int has_isa = rte_cpu_get_flag_enabled(RTE_CPUFLAG);    \
+                VLOG_DBG("CPU flag %s, available %s\n",                 \
+                         name_str, has_isa ? "yes" : "no");             \
+                isa_check_##RTE_CPUFLAG = ISA_CHECK_DONE_BIT;           \
+                if (has_isa) {                                          \
+                    isa_check_##RTE_CPUFLAG |= ISA_AVAILABLE_BIT;       \
+                }                                                       \
+            }                                                           \
+            if (isa_check_##RTE_CPUFLAG & ISA_AVAILABLE_BIT) {          \
+                return true;                                            \
+            }                                                           \
         }                                                               \
     } while (0)
 
-- 
2.25.1