A Programmer’s Hunch
The product I work on has been migrated from VC71 to VC90. Ever since the upgrade, I feel that the software is taking longer to start up, has become less responsive. I have been working on the software for several years, so I have certain performance expectations . My programmer’s hunch tells me that something just isn’t right.
I did some searches, and found out that Checked Iterator (Secure SCL) for STL has been turned on since VC80. It is enabled by default for Debug and Release build. There are numerous performance complains for VC80 STL implementation. Our product relies extensively on STL, so that could certainly be a contributing factor to the sluggishness.
Time to Test
To see the current state of the system, I wanted to see the performance between VC71 and VC90 with Checked Iterator. I also wanted the difference without Checked Iterator. Lastly, I threw in STLport into the pot, just because I found a blog that says it is the fastest.
In the test, I chose four commonly used containers in our software – vector, string, map and deque. For each container type, it will be run against two types of test – Iteration and Size. For the iteration test, the container will be benchmarked with a fixed size across a large number of iterations. For the size test, the size of the container grows while the number of iteration remains the same.
Comparison – Vector
The test for vector involves three operations – inseration, iterator traversal, and copy.
VC90 with Checked Iterator runs much slower.
Without Checked Iterator, much of the lost performance are regained.
From VC71 to VC90 with SCL, there are 70% – 100% decrease in performance. By turning off Checked Iterator, the performance of VC90 is roughly equivalent to VC71. STLport outperforms all versions of Visual Studio.
Comparison – String
The test for string involves three operations – string copy, substring search, and concatenation.
VC90 performed poorly compare to VC71, regardless of Checked Iterators.
STLport smoked its competitions in the short string test. (Note: 140 is the maximum character in a Twitter post)
Performance of string in VC90 degrades rapidly as the string grows. It appears that the Checked Iterator feature does not impact the performance of string.[Update: Secure SCL and HID was not turned off in string. See article.] Again, STLport outperforms all version of Visual Studios. This is likely because of the optimization from Short String Optimization and Template Expression for string concatenation.
Comparison – Map
The test for map involves insertion, search, and deletion.
Minor improvement in VC9 compare to VC71.
VC90 without Checked Iterator came out slightly ahead.
Surprisingly, the performance came out roughly the same for all, with VC71 to be the slowest.
Comparison – Deque
The test for Deque comes with a twist. The deque is implemented is as a priority queue through make_heap(), push_heap() and pop_heap(). Random items are inserted and removed from the queue upon each iteration.
As the deque grows, VC90 with Checked Iterator runs at snail pace.
VC71 and STLport came out fastest.
The performance for VC90 with Checked Iterator is quite disappointing compare to others.
So.. Now What?
VC90 with Checked Iterator is indeed very slow. Although I see the benefit of iterator validation during debug phase, I fail to understand why it is enabled in release build. I am not convinced by the argument of correctness over performance. Once the iterators are proven correct, Checked Iterator is simply a burden. When the software is in customers’ hand, all these validations are pointless.
On a side note, the string and vector performance of STLport is very impressive. It is more 2x faster than Visual Studio. It’s simply amazing.
The source and the results can be downloaded here.
Tools: Visual Studio 2003, Visual Studio 2008, STLport 5.2.1 (with Visual Studio 2008)
Machine Specification: Core Duo T2300 1.66 GHz with 2GB of RAM. Window XP SP3.