IE9 Javascript slower than IE8 - that's weird!

Question

I'm having difficulty in explaining why the following code runs slower in IE9 than IE8!

Here's some test code that runs smoothly in about half a second in (latest) FF/Chrome/Safari on OS X, WinXP, and Win7 plus IE7 & 8 on WinXP (for simplicity I removed the tweak that makes it work in IE6).

For some reason I can't explain, it's awful in IE9, slow and clunky. Reducing the time for the setTimeout makes it a bit quicker but no less jerky.

I've tried removing and benchmarking a number of what might be the choke points (Math.min for example ... all with no change.

I'm stumped ... can anyone please point me in the right direction?... preferably one that does not require browser-sniffing?

Here's the test code ...

<div id = 'panel' class='noShow' style='background-color: #aaa;'>
    <div id = 'wrapper' class='slideWrapper'>
        <p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p><p>xxxxxxxxxxx</p>
    </div>
</div>


<script type = 'text/javaScript'>

    var e = document.getElementById('panel');
    var w = document.getElementById('wrapper');

    w.style.overflow = 'hidden';                                                
    w.style.height = '1px'; 
    var sh = w.scrollHeight;
    show();
    function show()
    {
        setTimeout(function()
           {
                w.style.height = Math.min(sh, (w.offsetHeight + Math.ceil(sh/15))) + 'px';  
                if(
                     (w.offsetHeight < sh)
                ) 
                {
                    show(e);
                }
                else 
                {
                    w.style.height = 'auto'; 
                }                       
        }, 20); 
    }   
</script>

Answer 1

IE9默认在VMware Virtual Machines上进行软件渲染（截至2011年7月8日），应该会在不久的将来发布此修补程序，但此博客文章未提供时间表。

Answer 2

There are always odd performance variations when running in a virtualized environment. The selection of drivers and how the software offloads the processing will have an impact. Have you tried updating the drivers on your system?

Answer 3

Are you running the 64 bit version of IE 9 or the 32 bit version? The 64 bit version is not running Chakra which is the optimized JavaScript engine from the 32 bit version