MSIME support causing slow setup until explorer.exe paused?

[Dan Kegel]

I tried installing StarUML (after doing winetricks vcrun6 msxml3, as required),
and the setup crept along very slowly... so I got curious and ran top.
Most of the cpu time was being used by Explorer and wineserver,
and interestingly, if I suspended Explorer by doing
  strace -p <pid of explorer>
and then pressing ^S, the install ran awful darn fast.

So, what was explorer doing that was slowing things down so much?

writev(3, [{"l\0\0\0\30\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
64}, {"M\0S\0I\0M\0E\0S\0e\0r\0v\0i\0c\0e\0", 24}], 2) = 88
...
writev(3, [{"l\0\0\0*\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
64}, {"M\0S\0I\0M\0E\0R\0e\0c\0o\0n\0v\0e\0r\0t\0O\0p\0"..., 42}], 2)
= 106
...
writev(3, [{"l\0\0\0&\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
64}, {"M\0S\0I\0M\0E\0M\0o\0u\0s\0e\0O\0p\0e\0r\0a\0t\0"..., 38}], 2)
= 102
...
writev(3, [{"l\0\0\0*\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
64}, {"M\0S\0I\0M\0E\0R\0e\0c\0o\0n\0v\0e\0r\0t\0R\0e\0"..., 42}], 2)
= 106
...

This persisted in the app, too, not just in the installer.

So it kind of sounds like our msime support is hurting us performance-wise?
- Dan