portable sched_getcpu calls

Summary:
- added a feature test in build_detect_platform to check whether sched_getcpu() is available. glibc offers it only on some platforms (e.g., linux but not mac); this way should be easier than maintaining a list of platforms on which it's available.
- refactored PhysicalCoreID() to be simpler / less repetitive. ordered the conditional compilation clauses from most-to-least preferred
Closes https://github.com/facebook/rocksdb/pull/2272

Differential Revision: D5038093

Pulled By: ajkr

fbshipit-source-id: 81d7db3cc620250de220bdeb3194b2b3d7673de7

TARGETS

@@ -9,6 +9,7 @@ rocksdb_compiler_flags = [
   "-DROCKSDB_LIB_IO_POSIX",
   "-DROCKSDB_FALLOCATE_PRESENT",
   "-DROCKSDB_MALLOC_USABLE_SIZE",
+  "-DROCKSDB_SCHED_GETCPU_PRESENT",
   "-DOS_LINUX",
   # Flags to enable libs we include
   "-DSNAPPY",

build_tools/build_detect_platform

@@ -401,6 +401,17 @@ EOF
     if [ "$?" = 0 ]; then
         COMMON_FLAGS="$COMMON_FLAGS -DROCKSDB_RANGESYNC_PRESENT"
     fi
+
+    # Test whether sched_getcpu is supported
+    $CXX $CFLAGS -x c++ - -o /dev/null 2>/dev/null  <<EOF
+      #include <sched.h>
+      int main() {
+        int cpuid = sched_getcpu();
+      }
+EOF
+    if [ "$?" = 0 ]; then
+        COMMON_FLAGS="$COMMON_FLAGS -DROCKSDB_SCHED_GETCPU_PRESENT"
+    fi
 fi
 
 # TODO(tec): Fix -Wshorten-64-to-32 errors on FreeBSD and enable the warning.

build_tools/fbcode_config.sh

@@ -128,7 +128,7 @@ else
 fi
 
 CFLAGS+=" $DEPS_INCLUDE"
-CFLAGS+=" -DROCKSDB_PLATFORM_POSIX -DROCKSDB_LIB_IO_POSIX -DROCKSDB_FALLOCATE_PRESENT -DROCKSDB_MALLOC_USABLE_SIZE"
+CFLAGS+=" -DROCKSDB_PLATFORM_POSIX -DROCKSDB_LIB_IO_POSIX -DROCKSDB_FALLOCATE_PRESENT -DROCKSDB_MALLOC_USABLE_SIZE -DROCKSDB_SCHED_GETCPU_PRESENT"
 CXXFLAGS+=" $CFLAGS"
 
 EXEC_LDFLAGS=" $SNAPPY_LIBS $ZLIB_LIBS $BZIP_LIBS $LZ4_LIBS $ZSTD_LIBS $GFLAGS_LIBS $NUMA_LIB $TBB_LIBS"

build_tools/fbcode_config4.8.1.sh

@@ -93,7 +93,7 @@ else
 fi
 
 CFLAGS+=" $DEPS_INCLUDE"
-CFLAGS+=" -DROCKSDB_PLATFORM_POSIX -DROCKSDB_LIB_IO_POSIX -DROCKSDB_FALLOCATE_PRESENT -DROCKSDB_MALLOC_USABLE_SIZE"
+CFLAGS+=" -DROCKSDB_PLATFORM_POSIX -DROCKSDB_LIB_IO_POSIX -DROCKSDB_FALLOCATE_PRESENT -DROCKSDB_MALLOC_USABLE_SIZE -DROCKSDB_SCHED_GETCPU_PRESENT"
 CFLAGS+=" -DSNAPPY -DGFLAGS=google -DZLIB -DBZIP2 -DLZ4 -DZSTD -DNUMA -DTBB"
 CXXFLAGS+=" $CFLAGS"
 

db/db_test2.cc

@@ -1644,7 +1644,7 @@ size_t GetEncodedEntrySize(size_t key_size, size_t value_size) {
 TEST_F(DBTest2, ReadAmpBitmap) {
   Options options = CurrentOptions();
   BlockBasedTableOptions bbto;
-  size_t bytes_per_bit[2] = {1, 16};
+  uint32_t bytes_per_bit[2] = {1, 16};
   for (size_t k = 0; k < 2; k++) {
     // Disable delta encoding to make it easier to calculate read amplification
     bbto.use_delta_encoding = false;

port/port_posix.cc

@@ -16,6 +16,7 @@
 #include <cpuid.h>
 #endif
 #include <errno.h>
+#include <sched.h>
 #include <signal.h>
 #include <stdio.h>
 #include <string.h>
@@ -137,28 +138,26 @@ void RWMutex::ReadUnlock() { PthreadCall("read unlock", pthread_rwlock_unlock(&m
 
 void RWMutex::WriteUnlock() { PthreadCall("write unlock", pthread_rwlock_unlock(&mu_)); }
 
-int GetCPUID() {
+int PhysicalCoreID() {
+#if defined(ROCKSDB_SCHED_GETCPU_PRESENT) && defined(__x86_64__) && \
+    (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 22))
+  // sched_getcpu uses VDSO getcpu() syscall since 2.22. I believe Linux offers VDSO
+  // support only on x86_64. This is the fastest/preferred method if available.
   int cpuno = sched_getcpu();
   if (cpuno < 0) {
     return -1;
   }
-  else {
-    return cpuno;
-  }
-}
-
-int PhysicalCoreID() {
-#if defined(__i386__) || defined(__x86_64__)
-#if defined(__x86_64__) && (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 22))
-  return GetCPUID();
-#endif
+  return cpuno;
+#elif defined(__x86_64__) || defined(__i386__)
+  // clang/gcc both provide cpuid.h, which defines __get_cpuid(), for x86_64 and i386.
   unsigned eax, ebx = 0, ecx, edx;
   if (!__get_cpuid(1, &eax, &ebx, &ecx, &edx)) {
     return -1;
   }
   return ebx >> 24;
 #else
-  return GetCPUID();
+  // give up, the caller can generate a random number or something.
+  return -1;
 #endif
 }