Question

We are using the following method to write the log to log file. The log entries are kept in a vector named m_LogList (stl string entries are kept in the vector). The method is called when the size of the vector is more than 100. The CPU utilization of the Log server is around 20-40% if we call FlushLog method. If we comment out the FlushLog method, the CPU utilisation drops to 10-20% range.
What optimizations can I use to reduce the CPU utilization? We are using fstream object for writing the log entries to file

void CLogFileWriter::FlushLog()
{
    CRCCriticalSectionLock lock(m_pFileCriticalSection);
    //Entire content of the vector are writing to the file
    if(0 < m_LogList.size())
    {       
        for (int i = 0; i < (int)m_LogList.size(); ++i)
        {
            m_ofstreamLogFile << m_LogList[i].c_str()<<endl;
            m_nSize = m_ofstreamLogFile.tellp();

            if(m_pLogMngr->NeedsToBackupFile(m_nSize))
            {
                         // Backup the log file
            }
        }

        m_ofstreamLogFile.flush();
        m_LogList.clear(); //Clearing the content of the Log List           
    }
}

Answer 1

The first optimization I’d use is to drop the .c_str() in << m_LogList[i].c_str(). It forces operator<< to do a strlen (O(n)) instead of relying on string::size (O(1)).

Also, I’d just sum string sizes, instead of calling tellp.

Finally, << endl includes a flush, on every line. Just use << '\n'. You already have the flush at the end.