On Sat, Oct 17, 2015 at 12:20 AM, Dmitry Orlov <alepho...@gmail.com> wrote:
> Thanks Jacob!
>
> On 16 October 2015 at 13:56, Jakob Kummerow <jkumme...@chromium.org>
> wrote:
>
>> It's not about what the "internal array representation" is, it's about
>> how the array is accessed. V8 employs all sorts of smarts to make
>> JavaScript execution very fast, because that's its job. Accessing things
>> via the C++ API ("array->Set(...)" in your example) isn't anywhere near as
>> optimized. The difference is most pronounced for tight hot loops, it will
>> be much smaller (to the point of being negligible) for code that runs only
>> once.
>>
> Is there any way to bulk-allocate a v8::Array in a cheap way, for example,
> from a C-array of v8::Handle<v8::Value>s?
>
The fastest way to exchange large amounts of data between C++ and JS is
probably an externalized
<https://chromium.googlesource.com/v8/v8/+/master/include/v8.h#3472>
ArrayBuffer,
which allows access to its raw backing store on the C++ side, and a
TypedArray on top of it on the JS side.
> That said, if "Build Type: DEBUG" in your output means what I think it
>> means, then any performance measurement results are pretty much
>> meaningless. Try again in Release mode.
>>
> This message is reported because the Google benchmark library was build
> without NDEBUG directive:
>
> https://github.com/google/benchmark/blob/cf40a0f1172afc061e910eb5590f71e6ffdece66/src/console_reporter.cc#L43
> Apparently, that is the way its Makefile is written.
>
> My code is compiled wtih -O3:
> CXXFLAGS=-Wall -Werror -g -O3 -march=corei7 -mtune=corei7-avx -std=gnu++0x
> -pthread
>
> Is it possible that I inadvertently built V8 in debug mode? This is how I
> install it:
> $ export PATH=$PATH:/path/to/depot_tools
> $ fetch v8
> $ cd v8
> $ git fetch
> $ git checkout 4.2.77.21
>
You should update, 4.2 is outdated and unmaintained. branch-heads/4.6 is a
good choice right now (tip of the branch that's used in Chrome's Stable
channel).
> $ gclient sync
> $ make clean
> $ make -j8 native
>
OK, "make native" builds V8 in Release mode.
>
>> On Fri, Oct 16, 2015 at 8:57 PM, Dmitry Orlov <alepho...@gmail.com>
>> wrote:
>>
>>> Hello everyone,
>>>
>>> I've noticed peculiar performance characteristics of V8 objects when
>>> benchmarking my V8-embedding application. In particular, v8::Array is
>>> incredibly expensive - each Set(index, value) operation on an array
>>> consistently takes 100ns on a 3.4Ghz Xeon, instead of single digit
>>> nanoseconds one would expect from a C-array based implementation.
>>> In contrast, javascript code using arrays runs blaze-fast, taking around
>>> 2ns for each assignment.
>>>
>>> I've benchmarked these code fragments separately, implementation is
>>> below:
>>>
>>> void allocate_v8_integer_array(benchmark::State& state) {
>>> v8::HandleScope scope(isolate);
>>> v8::Local<v8::Value> int_value = v8::Integer::New(isolate, 100);
>>> while (state.KeepRunning()) {
>>> const int n = state.range_x();
>>> v8::Local<v8::Array> array = v8::Array::New(isolate,
>>> state.range_x());
>>> for (int i = 0; i < n; ++i) {
>>> array->Set(i, int_value);
>>> }
>>> }
>>> }
>>>
>>> void allocate_v8_integer_array_in_javascript(benchmark::State& state) {
>>> v8::TryCatch try_catch(isolate);
>>> v8::HandleScope scope(isolate);
>>> v8::Local<v8::Script> script =
>>> v8::Script::Compile(v8::String::NewFromUtf8(isolate,
>>> "function run(n) {"
>>> " var x = Array(n);"
>>> " for (var i = 0; i < n; i++) {"
>>> " x[i] = i;"
>>> " }"
>>> "}"));
>>> script->Run();
>>> assert(!try_catch.HasCaught());
>>> v8::Local<v8::Function> run = v8::Local<v8::Function>::Cast(
>>>
>>> context.Get(isolate)->Global()->Get(v8::String::NewFromUtf8(isolate,
>>> "run")));
>>> v8::Local<v8::Value> arg = v8::Integer::New(isolate,
>>> state.range_x());
>>> while (state.KeepRunning()) {
>>> run->Call(context.Get(isolate)->Global(), 1, &arg);
>>> assert(!try_catch.HasCaught());
>>> }
>>> }
>>>
>>> Benchmark results:
>>> Run on (8 X 3399.98 MHz CPU s
>>> 2015-10-16 18:47:44
>>> Build Type: DEBUG
>>> Benchmark Time(ns) CPU(ns)
>>> Iterations
>>>
>>> ---------------------------------------------------------------------------------
>>> allocate_v8_integer_array/1 190 190
>>> 3688287
>>> allocate_v8_integer_array/10 1061 1061
>>> 659836
>>> allocate_v8_integer_array/100 9936 9930
>>> 70495
>>> allocate_v8_integer_array/1000 96517 96458
>>> 7259
>>> allocate_v8_integer_array/9.76562k 967739 967146
>>> 724
>>> allocate_v8_integer_array_in_javascript/10 487 486
>>> 3104447
>>> allocate_v8_integer_array_in_javascript/100 1075 1074
>>> 1000000
>>> allocate_v8_integer_array_in_javascript/1000 3576 3573
>>> 264306
>>> allocate_v8_integer_array_in_javascript/9.76562k 22218 22204
>>> 33641
>>>
>>> Note how allocate_v8_integer_array asymptotes at 100ns per array
>>> assignment, where allocate_v8_integer_array_in_javascript asymptotes at 2ns
>>> per assignment.
>>> I would expect v8::Array to be the internal array representation for the
>>> javascript too. Is that not the case? Why the performance difference is so
>>> high?
>>>
>>> Thank you very much!
>>> Dmitry.
>>>
>>> --
>>> --
>>> v8-users mailing list
>>> v8-users@googlegroups.com
>>> http://groups.google.com/group/v8-users
>>> ---
>>> You received this message because you are subscribed to the Google
>>> Groups "v8-users" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to v8-users+unsubscr...@googlegroups.com.
>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>
>> --
>> --
>> v8-users mailing list
>> v8-users@googlegroups.com
>> http://groups.google.com/group/v8-users
>> ---
>> You received this message because you are subscribed to a topic in the
>> Google Groups "v8-users" group.
>> To unsubscribe from this topic, visit
>> https://groups.google.com/d/topic/v8-users/_fuFjcsktzc/unsubscribe.
>> To unsubscribe from this group and all its topics, send an email to
>> v8-users+unsubscr...@googlegroups.com.
>> For more options, visit https://groups.google.com/d/optout.
>>
>
> --
> --
> v8-users mailing list
> v8-users@googlegroups.com
> http://groups.google.com/group/v8-users
> ---
> You received this message because you are subscribed to the Google Groups
> "v8-users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to v8-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>
--
--
v8-users mailing list
v8-users@googlegroups.com
http://groups.google.com/group/v8-users
---
You received this message because you are subscribed to the Google Groups
"v8-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to v8-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
