Messages in this thread | | | Date | Tue, 23 Mar 2010 10:45:08 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge regression in performance |
| |
On Tue, 23 Mar 2010, Ingo Molnar wrote: > > It shows a very brutal amount of page fault invoked mmap_sem spinning > overhead.
Isn't this already fixed? It's the same old "x86-64 rwsemaphores are using the shit-for-brains generic version" thing, and it's fixed by
1838ef1 x86-64, rwsem: 64-bit xadd rwsem implementation 5d0b723 x86: clean up rwsem type system 59c33fa x86-32: clean up rwsem inline asm statements
NOTE! None of those are in 2.6.33 - they were merged afterwards. But they are in 2.6.34-rc1 (and obviously current -git). So Anton would have to compile his own kernel to test his load.
We could mark them as stable material if the load in question is a real load rather than just a test-case. On one of the random page-fault benchmarks the rwsem fix was something like a 400% performance improvement, and it was apparently visible in real life on some crazy SGI "initialize huge heap concurrently on lots of threads" load.
Side note: the reason the spinlock sucks is because of the fair ticket locks, it really does all the wrong things for the rwsem code. That's why old kernels don't show it - the old unfair locks didn't show the same kind of behavior.
Linus
| |