Performance issue with C++ STL

Well I ran this below code block for both STL vector and static array .

The difference in 700usec in a loop of 1000 iteration. Even using O2 did not improve the timing.

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typedef vector<RlcPduRecvBuffer *> RlcPduRecvBufferT;

RlcPduRecvBufferT rlcPduRecvBufferList;

//RlcPduRecvBuffer* rlcPduRecvBufferList[1000]; /** for Array **/

for(int j = 0;j<5;j++)
{
    Log_write1(UIABenchmark_start, (xdc_IArg)"process_sous_STL1");

    for(int i = 0;i<1000;i++)
    {
        RlcPduRecvBuffer *pRlcPduRecvBuffer = new RlcPduRecvBuffer();
       rlcPduRecvBufferList.push_back(pRlcPduRecvBuffer);
      //rlcPduRecvBufferList[i] = pRlcPduRecvBuffer; /** for Array **/
     delete rlcPduRecvBufferList[i];
    }

   Log_write1(UIABenchmark_stop, (xdc_IArg)"process_sous_STL1");

}

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Please let me know if i am missing something here as the understanding was with STL the performace wont degrade.

700usec difference is a huge diff considering the time criticality our app has.

regards

Soumya

Hi,

I suppose the overhead is due to the reallocatoin of the vector, triggered when you exaust the capacity.

In this case, the push_back() enlarge the vector by a 50% and then, if required, copy the original vector to the new one and free the old one. Due to the "new" insisde the lopp and depending on the implementation of the freestore manager, the copy could accurs at every reallocation.

Just to verify the performance, try to reserve the expected vector dimension (rlcPduRecvBufferList.reserve(1000*5)).

Well I can check that but that wont serve my purpose. Reserving static memory for vector is equivalent of a static array.

So I guess the final word is overhead of STL will take more time compared to non-STL data structures

But my understanding from first reply was STL with both use and overhead will not make any difference in time compared to other data structures in c++

regards

Soumya

It's not the same as a static array.  Even when you use "reserve", the array can still grow beyond that size.  Reserve is a performance optimization hint.