From b42dcb0eeb2d2c302b0ecabbc1092605a54213d6 Mon Sep 17 00:00:00 2001 From: Anna Henningsen Date: Mon, 25 Feb 2019 02:32:51 +0100 Subject: [PATCH] build: remove v8_typed_array_max_size_in_heap option MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This was added in 16f86d6c578ff7aec708c7d736558a199d290e9c, based on the assumption that otherwise, the memory behind `ArrayBuffer` instances could be moved around on the heap while native code holds references to it. This does not match what V8 actually does (and also did at the time): - The option/build variable was about always only about TypedArrays, not ArrayBuffers. Calls like `new ArrayBuffer(4)` call into C++ regardless of the option value, but calls like `new Uint8Array(4)` would not call into C++ under V8 defaults. - When first accessing a heap-allocated TypedArray’s `ArrayBuffer`, whether that is through the JS `.buffer` getter or the C++ `ArrayBufferView::Buffer()` function, a copy of the contents is created using the ArrayBuffer allocator and stored as the (permanent, unmovable) backing store. As a consequence, the memory returned by `ArrayBuffer::GetContents()` is not moved around, because it is fixed once the `ArrayBuffer` object itself first comes into explicit existence in any way. Removing this build option significantly speeds up creation of typed arrays from JS: $ ./node benchmark/compare.js --new ./node --old ./node-master --runs 10 --filter buffer-creation.js buffers | Rscript benchmark/compare.R confidence improvement accuracy (*) (**) (***) buffers/buffer-creation.js n=1024 len=10 type='buffer()' *** 593.66 % ±28.64% ±41.10% ±60.36% buffers/buffer-creation.js n=1024 len=10 type='fast-alloc-fill' *** 675.42 % ±90.67% ±130.24% ±191.54% buffers/buffer-creation.js n=1024 len=10 type='fast-alloc' *** 663.55 % ±58.41% ±83.87% ±123.29% buffers/buffer-creation.js n=1024 len=10 type='fast-allocUnsafe' 3.10 % ±9.63% ±13.22% ±18.07% buffers/buffer-creation.js n=1024 len=10 type='slow-allocUnsafe' 4.67 % ±5.55% ±7.77% ±10.97% buffers/buffer-creation.js n=1024 len=10 type='slow' -2.48 % ±4.47% ±6.12% ±8.34% buffers/buffer-creation.js n=1024 len=1024 type='buffer()' -1.91 % ±4.71% ±6.45% ±8.79% buffers/buffer-creation.js n=1024 len=1024 type='fast-alloc-fill' -1.34 % ±7.53% ±10.33% ±14.10% buffers/buffer-creation.js n=1024 len=1024 type='fast-alloc' 0.52 % ±5.00% ±6.87% ±9.40% buffers/buffer-creation.js n=1024 len=1024 type='fast-allocUnsafe' 0.39 % ±5.65% ±7.78% ±10.67% buffers/buffer-creation.js n=1024 len=1024 type='slow-allocUnsafe' -0.13 % ±5.68% ±7.83% ±10.77% buffers/buffer-creation.js n=1024 len=1024 type='slow' -5.07 % ±7.15% ±9.80% ±13.35% buffers/buffer-creation.js n=1024 len=2048 type='buffer()' 0.57 % ±2.70% ±3.74% ±5.16% buffers/buffer-creation.js n=1024 len=2048 type='fast-alloc-fill' -1.60 % ±4.96% ±6.79% ±9.25% buffers/buffer-creation.js n=1024 len=2048 type='fast-alloc' 1.29 % ±3.79% ±5.20% ±7.09% buffers/buffer-creation.js n=1024 len=2048 type='fast-allocUnsafe' 2.73 % ±8.79% ±12.05% ±16.41% buffers/buffer-creation.js n=1024 len=2048 type='slow-allocUnsafe' -0.99 % ±6.27% ±8.65% ±11.91% buffers/buffer-creation.js n=1024 len=2048 type='slow' -5.98 % ±6.24% ±8.71% ±12.20% buffers/buffer-creation.js n=1024 len=4096 type='buffer()' -1.75 % ±3.48% ±4.78% ±6.56% buffers/buffer-creation.js n=1024 len=4096 type='fast-alloc-fill' -3.18 % ±3.97% ±5.45% ±7.45% buffers/buffer-creation.js n=1024 len=4096 type='fast-alloc' 2.05 % ±4.05% ±5.58% ±7.65% buffers/buffer-creation.js n=1024 len=4096 type='fast-allocUnsafe' 1.44 % ±5.51% ±7.63% ±10.57% buffers/buffer-creation.js n=1024 len=4096 type='slow-allocUnsafe' * -4.77 % ±4.30% ±5.90% ±8.06% buffers/buffer-creation.js n=1024 len=4096 type='slow' -3.31 % ±6.38% ±8.86% ±12.34% buffers/buffer-creation.js n=1024 len=8192 type='buffer()' 0.06 % ±2.70% ±3.77% ±5.31% buffers/buffer-creation.js n=1024 len=8192 type='fast-alloc-fill' -1.20 % ±3.30% ±4.53% ±6.17% buffers/buffer-creation.js n=1024 len=8192 type='fast-alloc' -1.46 % ±2.75% ±3.84% ±5.38% buffers/buffer-creation.js n=1024 len=8192 type='fast-allocUnsafe' 1.27 % ±4.69% ±6.49% ±8.98% buffers/buffer-creation.js n=1024 len=8192 type='slow-allocUnsafe' -1.68 % ±3.30% ±4.62% ±6.49% buffers/buffer-creation.js n=1024 len=8192 type='slow' -2.49 % ±3.24% ±4.44% ±6.07% (Re-running the outlier with 30 runs instead of 10:) buffers/buffer-creation.js n=1024 len=4096 type='slow-allocUnsafe' 2.06 % ±2.39% ±3.19% ±4.15% The performance gains effect are undone once native code accesses the underlying ArrayBuffer, but then again that a) does not happen for all TypedArrays, and b) it should also make sense to look into using `ArrayBufferView::CopyContents()` in some places, which is made specifically to avoid such a performance impact and allows us to use the benefits of heap-allocated typed arrays. Refs: https://github.com/nodejs/node/commit/16f86d6c578ff7aec708c7d736558a199d290e9c Refs: https://github.com/nodejs/node/pull/2893 Refs: https://github.com/nodejs/node/commit/74178a5682958d499896e0fa1af6bc0321ec1935#commitcomment-13250880 Refs: http://logs.libuv.org/node-dev/2015-09-15 PR-URL: https://github.com/nodejs/node/pull/26301 Reviewed-By: Matteo Collina Reviewed-By: James M Snell --- configure.py | 4 ---- 1 file changed, 4 deletions(-) diff --git a/configure.py b/configure.py index a3f885c0fd0d8f..ac6b3d4788cd1b 100755 --- a/configure.py +++ b/configure.py @@ -1123,10 +1123,6 @@ def configure_v8(o): o['variables']['node_use_bundled_v8'] = b(not options.without_bundled_v8) o['variables']['force_dynamic_crt'] = 1 if options.shared else 0 o['variables']['node_enable_d8'] = b(options.enable_d8) - # Unconditionally force typed arrays to allocate outside the v8 heap. This - # is to prevent memory pointers from being moved around that are returned by - # Buffer::Data(). - o['variables']['v8_typed_array_max_size_in_heap'] = 0 if options.enable_d8: o['variables']['test_isolation_mode'] = 'noop' # Needed by d8.gyp. if options.without_bundled_v8 and options.enable_d8: