Re: [boost] [review] The review of Boost.DoubleEnded starts today: September 21 - September 30

Subject: Re: [boost] [review] The review of Boost.DoubleEnded starts today: September 21 - September 30
From: Benedek Thaler (thalerbenedek_at_[hidden])
Date: 2017-10-02 22:02:03

On Mon, Oct 2, 2017 at 7:30 PM, Thorsten Ottosen <tottosen_at_[hidden]>
wrote:

> Hi,
>
> Some more points to consider. I tried comparing push_back/unsafe_push_back
> a little. I don't see any performance speedup on my system if the loop body
> is just the push_back. If I make the loop a little more complicated than
> just a push_back, I get some differences:
>
> Hi,

My concern with the above benchmark, is that it does not compare the same
thing: it calls reserve here but not there (std::deque and
boost::container::deque have no reserve).

I tried a similar test, comparing devector/vector/container.vector
unsafe_push_back/push_back, using google benchmark. See the code attached.
This is how I run it:

$ uname -r
3.13.0-24-generic
$ g++ ---version
g++-5 (Ubuntu 5.4.1-2ubuntu1~14.04) 5.4.1 20160904
$ g++ -Wall -Werror -Wextra -std=c++11 -O2 -march=native -I ../include/ -I
../../google-benchmark/include/ -I $BOOST_BUILD_PATH -L
../../google-benchmark/src/ google_push_back.cpp -DNDEBUG  -lbenchmark
-lpthread

$ sudo su
# echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
# nice -20 taskset -c 0 ./a.out
Run on (8 X 3500 MHz CPU s)
2017-10-02 23:55:35
***WARNING*** CPU scaling is enabled, the benchmark real time measurements
may be noisy and will incur extra overhead.
(I consider this warning a false positive. CPU0 has no scaling, and this
task is pinned there)
-----------------------------------------------------------------------
Benchmark                                Time           CPU Iterations
-----------------------------------------------------------------------
devector_unsafe_push_back/8            785 ns        782 ns     897711
devector_unsafe_push_back/64           846 ns        844 ns     819441
devector_unsafe_push_back/512         1219 ns       1216 ns     582811
devector_unsafe_push_back/4096        4207 ns       4238 ns     164192
devector_unsafe_push_back/32768      30885 ns      30876 ns      24689
vector_push_back/8                     796 ns        793 ns     890232
vector_push_back/64                    967 ns        965 ns     724603
vector_push_back/512                  2109 ns       2104 ns     335052
vector_push_back/4096                11279 ns      11300 ns      61336
vector_push_back/32768               84355 ns      84253 ns       8332
cvector_push_back/8                    791 ns        788 ns     883267
cvector_push_back/64                   861 ns        858 ns     809779
cvector_push_back/512                 1330 ns       1326 ns     527179
cvector_push_back/4096                5081 ns       5109 ns     135001
cvector_push_back/32768              34288 ns      34286 ns      20202

# echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

Re-run results in very similar results.
I think the numbers are convincing in favor of devector::unsafe_push_back.
Please repeat the test.

Thanks,
Benedek