Useful tips: making threads out of Tiger can be difficult (plus: Tenfourbird is awesome)

Because it has all these claws and sharp bits and it doesn't like being made into thread I have been displeased with the performance thus far of 22 after a while using it regularly (recall that I was on vacation in the beautiful Pacific Northwest and my iBook G4 usually runs 17 so that I can make sure the stable branch is still working well), and I think I finally know why. It's a manifestation, yet again, of Tiger's comparatively poor multithreading performance compared to Leopard and later kernels, the crux of which is issue 193 (and should hopefully be solved once and for all if I can get jemalloc functioning properly, which is issue 218). Unfortunately, the performance issues appear to be because of Mozilla's well-intentioned attempts to move stuff off the main thread, and of the local test systems the multi-processor Power Macs -- the ones you'd think would benefit most -- actually do tremendously worse with this approach in 10.4.

Permit me to demonstrate. If you're on a single processor Mac, going to Butterfly Labs (the reliable test case for this problem, though I'm sure there are others) is sluggish and beachballs a bit, though it eventually loads. My iMac G4 grinds into it after around 30 seconds, which is lousy, but bearable. Now do it on a multi processor Mac. On my 10.4 quad G5, it takes minutes despite having four times the cores, four times the L2 cache and 2.5 times the clock speed, even with processor performance set to Highest, during which the browser is unresponsive for long periods of time. That, to express it gently, sucks. After some exhaustive debugging I am fully convinced that this too is almost entirely due to inefficiencies in the Tiger kernel's implementation of pthreads. The processors just trip over each other trying to stay synced and the threads get starved for resources.

I am told that issue 193 does not affect 10.5 nearly as badly if at all as it does 10.4, so I've made a speculative fix to NSPR and JavaScript tracked as issue 231. Until I can get jemalloc to work correctly and solve the whole problem, the simplest stopgap solution seems to be to make TenFourFox believe there is only one processor on 10.4 systems, regardless of how many it actually has, which causes the browser not to attempt to spin things into multiple threads. (The patch checks Gestalt() to see if it it's on 10.4; if it isn't, it runs the normal processor detection code.) I'm typing this in such a build on the G5 and the weird intermittent stops and seizes I also observed with 22 are now nearly undetectable, even with the processors throttled to Reduced mode. 10.5 users, please try the reliable test site above on single and multi-processor Power Macs if you have them available. The difference should be extreme on the multi-processor Power Mac if 10.5 is affected by this also and if it is, then we just make it detect only one processor on any Power Mac until we can work around the poor kernel performance later. (jemalloc is number two on my priority list, behind, of course, BaselineCompiler/IonMonkey.) Either way, one form or another of this fix will appear in 22.0.1, which is the interim release to replace Fx23 while I work on Fx24. It won't help sites much that were already bad in previous versions, but it will definitely fix the accumulated regressions.

Other things. Now that Google has made Google Groups slow and hard to navigate, which I used to use for reading Mozilla newsgroups (though I guess that's better than what they did to Google Reader), I finally have an excuse to try Tenfourbird. Normally I read Usenet and E-mail from a shell prompt, but I decided to use Tenfourbird and talk to news.mozilla.org directly to see how well it works, and to keep those groups separate from my regular .newsrc file. And, well, wow. It's quick and fast, and seems pretty much bug-free. I am delighted to see that our anonymous builder in the land of the rising sun has kept pace with us, and I hope he makes the jump to 24 when we do. ありがとうございました。