xpcshell and reftest are slower on Win7, faster on WinXP

Why, oh why, would xpcshell and reftest run so significantly slower on Win7 vs on WinXP? The other unittest suites give comparable performance except for:

WinXP vs Win7

  • reftest: 50% slower (1,488 seconds on WinXP but 2,234 on Win7)
  • xpcshell: 75% slower (1,248 seconds on WinXP but 2,190 on Win7)

This was measured using the same binary build of Firefox, and the same identical hardware being used on both OS.

Also, this difference is *after* Armen and Jimm already landing one fix which really helped, but there’s obviously more to do – details can be found in Armen’s blog and also in bug#617503. Can you help?

Given the number of checkins (and hence tests) we run daily, any help fixing this will be a big win (groan!) for our Win7 test waittimes, which impacts us all.

2 thoughts on “xpcshell and reftest are slower on Win7, faster on WinXP”

  1. For reftest, here’s one theory (that would need to be tested). On Win7, contrary to WinXP, we have Direct2D acceleration. Although it’s generally a speed improvement, it also takes some time to initialize. The reftests render thousands of tiny pages, probably making initialization time very significant.

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