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WebPagetest vs. Keynote TxP/IE9 measurements
04-03-2013, 06:44 AM
Post: #2
RE: WebPagetest vs. Keynote TxP/IE9 measurements
Yes, WebPagetest uses an actual IE 9 browser to run the test. The architecture is pretty similar to Keynote's TxP agents and they should be pretty familiar with the WebPagetest agents as well. I know they are aware of them and when I was at AOL we actually provided Keynote some links to the WPT code for fixing issues that we were seeing in their agents.

It's hard to say for sure without knowing more but my guess is that it is related to the actual machines and how they are deployed. If I remember correctly, Keynote runs their TxP agents in multiple Windows Terminal Server sessions and runs several agents per machine.

The WebPagetest agents are stacked a little differently and run each tester in it's own VM (with multiple VMs on a physical machine). One key difference is that the WebPagetest machines run on SSD's to make sure that there is no I/O bottleneck from sharing I/O across multiple agents on a single machine.

Another possibility could be in how the browsers are instrumented where I believe they use the remote COM interfaces into IE while WPT uses code injection and runs directly inside of the browser. Not sure if there's some overhead introduced there.

Pretty much speculation on my part for what could be causing the gaps based on what I have seen before but yes, WebPagetest uses real browsers.
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RE: WebPagetest vs. Keynote TxP/IE9 measurements - pmeenan - 04-03-2013 06:44 AM

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