Re: [boost] [boost.chrono] Slow down process (if specifing c++11)

Subject: Re: [boost] [boost.chrono] Slow down process (if specifing c++11)
From: Gaetano Mendola (mendola_at_[hidden])
Date: 2013-09-06 06:16:20

On 09/06/2013 11:28 AM, Gaetano Mendola wrote:
> See my reply to Julien Ritard in the thread, just the simply
> call to boost chrono even as last operation in the main slows it
> down.
> 
> Regards
> Gaetano Mendola

In the mean time I have filled a bug with gcc:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58333

let see what they say.

Regards
Gaetano Mendola

> On 08/28/2013 10:48 PM, Vicente J. Botet Escriba wrote:
>> Le 26/08/13 15:54, Gaetano Mendola a écrit :
>>> Hi have tried the following code compiling it with gcc 4.6.3,
>>> with four combinations:
>>>
>>> 1) -O3
>>> 2) -O3 (commeting out the chrono call)
>>> 3) -O3 -std=c++0x
>>> 4) -O3 -std=c++0x (commenting out the chrono call)
>>>
>>> and I'm obtaining the following runtime values:
>>>
>>> 1) 8921 ms
>>> 2) 8915 ms
>>> 3) 9400 ms
>>> 4) 8933 ms
>>>
>>> as you can see the combination:  "c++11 and chrono call" slows down the entire
>>> process. I have tried the same with gcc 4.8.1 and all times are more or less
>>> the same.
>>>
>>> At this point I'm not sure if it's a problem of chrono with gcc 4.6.3 or
>>> simply an issue of 4.6.3 disappeared in 4.8.1 series.
>>>
>>> Regards
>>> Gaetano Mendola
>> I don't know if changing the order could changes the results.
>>
>>   gettimeofday(&myStart, 0);
>>
>>   boost::chrono::time_point<boost::chrono::steady_clock> t1 = boost::chrono::high_resolution_clock::now();
>>
>> and
>>
>>   std::cout << "t1: " << t1 << std::endl;
>>
>>   gettimeofday(&myStop, 0);
>>
>>   timersub(&myStop,&myStart,&myResult);
>>
>>   std::cout << "Time: " <<  myResult.tv_sec*1000 + myResult.tv_usec/1000.0 << std::endl;
>>
>>
>> Or to be neutral execute either the chrono computation either the timeval one.
>>
>> HTH,
>> Vicente
>>
>>>
>>> Here the code I have used:
>>>
>>> #include <iostream>
>>> #include <boost/chrono.hpp>
>>> #include <sys/time.h>
>>> #include <math.h>
>>>
>>>
>>> int main() {
>>>
>>>    cpu_set_t  myAffinityMask;
>>>    CPU_ZERO( &myAffinityMask );
>>>    CPU_SET(0, &myAffinityMask );
>>>    sched_setaffinity(0, sizeof(myAffinityMask), &myAffinityMask);
>>>
>>>    volatile float* myMemoryA = new float[(1<<24)];
>>>    volatile float* myMemoryB = new float[(1<<24)];
>>>
>>>    struct timeval myStart;
>>>    struct timeval myStop;
>>>    struct timeval myResult;
>>>
>>>    boost::chrono::time_point<boost::chrono::steady_clock> t1 = boost::chrono::high_resolution_clock::now();
>>>
>>>    gettimeofday(&myStart, 0);
>>>
>>>    for (size_t i = 0; i < (1<<24); ++i) {
>>>      myMemoryA[i] = i;
>>>      myMemoryB[i] = i+1;
>>>    }
>>>    delete []myMemoryA;
>>>    delete []myMemoryB;
>>>
>>>    for (size_t j = 0; j < 100; ++j) {
>>>      volatile float* myMemoryA = new float[(1<<24)];
>>>      volatile float* myMemoryB = new float[(1<<24)];
>>>      for (size_t i = 0; i < (1<<24); ++i) {
>>>        myMemoryA[i] *= sqrtf(myMemoryB[i]);
>>>      }
>>>      delete []myMemoryA;
>>>      delete []myMemoryB;
>>>    }
>>>    gettimeofday(&myStop, 0);
>>>
>>>    timersub(&myStop,&myStart,&myResult);
>>>
>>>    std::cout << "Time: " <<  myResult.tv_sec*1000 + myResult.tv_usec/1000.0 << std::endl;
>>>    std::cout << "t1: " << t1 << std::endl;
>>> }
>>>
>>>
>>>
>>>
>>
>>
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