Boris sent an email to mozilla.dev.performance regarding the unusable state of the Error Console on cairo builds. The text is copied below: ---------- So I discovered today that on trunk the error console takes _forever_ to open. To be precise, starting with a blank error console, then loading the following HTML: <script> for (var i = 0; i < 20; ++i) { setTimeout("throw 'This is a test of the emergency broadcast system; only a test and all that dudes'", 0); } </script> then opening the error console, I see it take 15-20 seconds for the window to appear. A profile shows that we're spending a _lot_ of time in reflow (pretty much all the time is in InitialReflow()) and of the reflow time about 90% is spent under nsTextFrame::MeasureText. Almost all of that is under gfxPangoTextRun::Measure, gfxPangoTextRun::~gfxPangoTextRun, and gfxPangoFontGroup::MakeTextRun (with these last two accoundting for about 15% of the MeasureText time, with the rest under Measure). The time under Measure is almost all gfxPangoTextRun::EnsurePangoLayout. Of particular interest is pango_context_get_base_dir, which takes up about 25% of total layout time. This seems to be doing a lot of mallocing, removing from font maps, creating new script iters, bsearch, hashtable lookups, utf8 to ucs4 conversion, etc... I see this in both Firefox and Seamonkey cairo builds. For comparison, the non-cairo builds open up the Error Console in about 4 seconds (which is _still_ ridiculous) when using the same testcase. So there is probably also the problem of us doing a _lot_ of reflow here for some reason. And of cairo making that about 5x slower... :( I'd be happy to mail the profile to anyone interested in it. Also of interest, a reflow branch non-cairo build opens the console about twice as fast as a trunk non-cairo build. I don't have a reflow branch cairo build on hand to test with, though. -Boris

Blocking the cross-platform cairo metabug for now. If the problem is only on Linux (unlikely, TBH) the correct blocking bug is bug 334720.

(In reply to comment #1) > Blocking the cross-platform cairo metabug for now. If the problem is only on > Linux (unlikely, TBH) the correct blocking bug is bug 334720. seems likely to me, given: > Almost all of that is under > gfxPangoTextRun::Measure, gfxPangoTextRun::~gfxPangoTextRun, and > gfxPangoFontGroup::MakeTextRun Which is only used on Linux (well, the rest of X11 too, and BeOS, and maybe OS/2?)

Is this still an issue? At least on Windows, error console comes up after only a short delay.

This does seem to be OK now with new-textframe and the reflow branch... > At least on Windows, This was a Linux-specific bug.

I came upon the bug when looking at bug 334719, so that's why I mentioned my platform :-)