Allow (and use) std::hardware_destructive_interference_size.

Bug: none
Change-Id: Ic3282588f4c6e75c7fcbff6f9c64827b5c18a10d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5767325
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Owners-Override: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1350762}

base/allocator/partition_allocator/src/partition_alloc/partition_address_space.h

@@ -6,6 +6,7 @@
 #define PARTITION_ALLOC_PARTITION_ADDRESS_SPACE_H_
 
 #include <cstddef>
+#include <new>
 #include <utility>
 
 #include "partition_alloc/address_pool_manager_types.h"
@@ -436,7 +437,8 @@ class PA_COMPONENT_EXPORT(PARTITION_ALLOC) PartitionAddressSpace {
   static constexpr uintptr_t kUninitializedPoolBaseAddress =
       static_cast<uintptr_t>(-1);
 
-  struct alignas(kPartitionCachelineSize) PA_THREAD_ISOLATED_ALIGN PoolSetup {
+  struct alignas(std::hardware_destructive_interference_size)
+      PA_THREAD_ISOLATED_ALIGN PoolSetup {
     // Before PartitionAddressSpace::Init(), no allocation are allocated from a
     // reserved address space. Therefore, set *_pool_base_address_ initially to
     // -1, so that PartitionAddressSpace::IsIn*Pool() always returns false.
@@ -466,7 +468,9 @@ class PA_COMPONENT_EXPORT(PARTITION_ALLOC) PartitionAddressSpace {
   static_assert(sizeof(PoolSetup) % SystemPageSize() == 0,
                 "PoolSetup has to fill a page(s)");
 #else
-  static_assert(sizeof(PoolSetup) % kPartitionCachelineSize == 0,
+  static_assert(sizeof(PoolSetup) %
+                        std::hardware_destructive_interference_size ==
+                    0,
                 "PoolSetup has to fill a cacheline(s)");
 #endif
 

base/allocator/partition_allocator/src/partition_alloc/partition_alloc_constants.h

@@ -75,15 +75,6 @@ using internal::FreeFlags;
 
 namespace internal {
 
-// Size of a cache line. Not all CPUs in the world have a 64 bytes cache line
-// size, but as of 2021, most do. This is in particular the case for almost all
-// x86_64 and almost all ARM CPUs supported by Chromium. As this is used for
-// static alignment, we cannot query the CPU at runtime to determine the actual
-// alignment, so use 64 bytes everywhere. Since this is only used to avoid false
-// sharing, getting this wrong only results in lower performance, not incorrect
-// code.
-constexpr size_t kPartitionCachelineSize = 64;
-
 // Underlying partition storage pages (`PartitionPage`s) are a power-of-2 size.
 // It is typical for a `PartitionPage` to be based on multiple system pages.
 // Most references to "page" refer to `PartitionPage`s.

base/allocator/partition_allocator/src/partition_alloc/partition_root.h

@@ -35,6 +35,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <limits>
+#include <new>
 #include <optional>
 #include <utility>
 
@@ -225,7 +226,7 @@ struct alignas(64) PA_COMPONENT_EXPORT(PARTITION_ALLOC) PartitionRoot {
   //
   // Careful! PartitionAlloc's performance is sensitive to its layout.  Please
   // put the fast-path objects in the struct below.
-  struct alignas(internal::kPartitionCachelineSize) Settings {
+  struct alignas(std::hardware_destructive_interference_size) Settings {
     // Chromium-style: Complex constructor needs an explicit out-of-line
     // constructor.
     Settings();
@@ -283,7 +284,7 @@ struct alignas(64) PA_COMPONENT_EXPORT(PARTITION_ALLOC) PartitionRoot {
 
   // Not used on the fastest path (thread cache allocations), but on the fast
   // path of the central allocator.
-  alignas(internal::kPartitionCachelineSize) internal::Lock lock_;
+  alignas(std::hardware_destructive_interference_size) internal::Lock lock_;
 
   Bucket buckets[internal::kNumBuckets] = {};
   Bucket sentinel_bucket{};

base/allocator/partition_allocator/src/partition_alloc/thread_cache.h

@@ -9,6 +9,7 @@
 #include <cstdint>
 #include <limits>
 #include <memory>
+#include <new>
 #include <optional>
 
 #include "partition_alloc/build_config.h"
@@ -604,7 +605,7 @@ PA_ALWAYS_INLINE void ThreadCache::PutInBucket(Bucket& bucket,
   // % 16. Its distance to the next cacheline is
   //   `64 - ((slot_start & 63) / 16) * 16`
   static_assert(
-      internal::kPartitionCachelineSize == 64,
+      std::hardware_destructive_interference_size == 64,
       "The computation below assumes that cache lines are 64 bytes long.");
   int distance_to_next_cacheline_in_16_bytes = 4 - ((slot_start >> 4) & 3);
   int slot_size_remaining_in_16_bytes = bucket.slot_size / 16;

components/media_router/common/providers/cast/channel/enum_table.h

@@ -12,6 +12,7 @@
 
 #include <cstdint>
 #include <cstring>
+#include <new>
 #include <optional>
 #include <ostream>
 #include <string_view>
@@ -367,8 +368,7 @@ class EnumTable {
 
  private:
 #ifdef ARCH_CPU_64_BITS
-  // Align the data on a cache line boundary.
+  alignas(std::hardware_destructive_interference_size)
-  alignas(64)
 #endif
       std::initializer_list<Entry> data_;
   bool is_sorted_;

styleguide/c++/c++-features.md

@@ -574,35 +574,6 @@ Overlaps with utilities in `base/strings/string_number_conversions.h`, which are
 easier to use correctly.
 ***
 
-### std::hardware_{con,de}structive_interference_size <sup>[banned]</sup>
-
-```c++
-struct SharedData {
-  ReadOnlyFrequentlyUsed data;
-  alignas(std::hardware_destructive_interference_size) std::atomic<size_t> counter;
-};
-```
-
-**Description:** The `std::hardware_destructive_interference_size` constant is
-useful to avoid false sharing (destructive interference) between variables that
-would otherwise occupy the same cacheline. In contrast,
-`std::hardware_constructive_interference_size` is helpful to promote true
-sharing (constructive interference), e.g. to support better locality for
-non-contended data.
-
-**Documentation:**
-[`std::hardware_destructive_interference_size`](https://en.cppreference.com/w/cpp/thread/hardware_destructive_interference_size),
-[`std::hardware_constructive_interference_size`](https://en.cppreference.com/w/cpp/thread/hardware_destructive_interference_size)
-
-**Notes:**
-*** promo
-Banned for now since these are
-[not supported yet](https://github.com/llvm/llvm-project/issues/60174). Allow
-once supported.
-
-[Discussion thread](https://groups.google.com/a/chromium.org/g/cxx/c/cwktrFxxUY4)
-***
-
 ### std::in_place{_type,_index}[_t] <sup>[banned]</sup>
 
 ```c++
@@ -1206,6 +1177,31 @@ avoiding the need to use the `erase(remove(...` paradigm.
 [Migration bug](https://crbug.com/1414639)
 ***
 
+### std::hardware_{con,de}structive_interference_size <sup>[allowed]</sup>
+
+```c++
+struct SharedData {
+  ReadOnlyFrequentlyUsed data;
+  alignas(std::hardware_destructive_interference_size) std::atomic<size_t> counter;
+};
+```
+
+**Description:** The `std::hardware_destructive_interference_size` constant is
+useful to avoid false sharing (destructive interference) between variables that
+would otherwise occupy the same cacheline. In contrast,
+`std::hardware_constructive_interference_size` is helpful to promote true
+sharing (constructive interference), e.g. to support better locality for
+non-contended data.
+
+**Documentation:**
+[`std::hardware_destructive_interference_size`](https://en.cppreference.com/w/cpp/thread/hardware_destructive_interference_size),
+[`std::hardware_constructive_interference_size`](https://en.cppreference.com/w/cpp/thread/hardware_destructive_interference_size)
+
+**Notes:**
+*** promo
+[Discussion thread](https://groups.google.com/a/chromium.org/g/cxx/c/cwktrFxxUY4)
+***
+
 ### std::is_[un]bounded_array <sup>[allowed]</sup>
 
 ```c++