加载事件日志时如何降低CPU利用率？

Question

I have a program that loads System's Event logs to a Hastable to be used. The problem is that it's utilizing 100% of the CPU. What is the best solution to lower the usage using API calls.

Hashtable currentLog = (Hashtable)_logs[l.Log];

foreach (EventLogEntry e in l.Entries)
{    
    if (_lastRun <= e.TimeWritten.ToUniversalTime() )
    {                                
        if (_verboseOutput)
        {
            Logger.TraceWrite(String.Format(
                                    "Source={0}, EventId={1}, Date/Time={2}, Message={3}", 
                                     e.Source, 
                                     e.EventID, 
                                     e.TimeWritten, 
                                     e.Message));
        }

        string key = GetEventKey(e);
        if (currentLog[key] == null)
        {
            currentLog[key] = e;
        }
    }
}

Answer 1

You can load logs in a separate thread with low priority ( Thread.Priority ):

Thread thread = new Thread(loadLogsMethod);
thread.Priority = ThreadPriority.BelowNormal;
thread.Start();

EDIT: By delegating execution to a separate thread you decrease average CPU load but total execution time will be increased.

Answer 2

It seems that before you go ahead and change your code it would be wise to perform some performance testing to see where the bottlenecks lie.

A question I asked a few months ago talks about the methods you can use to measure the performance of your application, as well as some of the considerations that you can make whilst doing so:

Function profiling woes - Visual Studio 2010 Ultimate

Answer 3

Usually, there is nothing wrong with 100% CPU use ¹ . All that means is that the processor is running at maximum for the duration of the operation. This is a good thing. Why waste time forcing the CPU to stop working? The OS is most likely a pre-emptive OS (since you've tagged c# it's likely to be Windows), so Polynomial's comment about stability is incorrect, the OS will switch tasks regardless of the load.

If you reduce the CPU use to 50% then the processing will take twice as long.

What you want to ask is "How can I reduce the time this algorithm takes" / "Is there a more efficient algorithm" since any algorithm you use will run at 100% until it completes.

It would help if you explain what you're trying to do here, perhaps there's a better way to do it.

Looking at the code, I think the biggest overhead is in the GetEventKey method, showing us that code may help.

1. 100% CPU usage in a GUI thread is generally a bad thing as the GUI could become unusable as the GUI thread has to wait until the method that's consuming the CPU finishes before handling user interaction.

Answer 4

The high CPU usage is probably due to the iterator having to walk the entire event log to check if there any new ones available. Try switching the foreach out and using a for instead. You can also try using the performance analysis tools in Visual Studio to see which line(s) are CPU hotspots.