| Date | Fri, 9 Apr 2010 14:14:21 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH 00/13] mm: preemptibility -v2 |
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On Thu, Apr 08, 2010 at 09:17:37PM +0200, Peter Zijlstra wrote: > Hi, > > This (still incomplete) patch-set makes part of the mm a lot more preemptible. > It converts i_mmap_lock and anon_vma->lock to mutexes. On the way there it > also makes mmu_gather preemptible. > > The main motivation was making mm_take_all_locks() preemptible, since it > appears people are nesting hundreds of spinlocks there. > > The side-effects are that we can finally make mmu_gather preemptible, something > which lots of people have wanted to do for a long time.
What's the straight-line performance impact of all this? And how about concurrency, I wonder. mutexes of course are double the atomics, and you've added a refcount which is two more again for those paths using it.
Page faults are very important. We unfortunately have some databases doing a significant amount of mmap/munmap activity too. I'd like to see microbenchmark numbers for each of those (both anon and file backed for page faults).
kbuild does quite a few pages faults, that would be an easy thing to test. Not sure what reasonable kinds of cases exercise parallelism.
> What kind of performance tests would people have me run on this to satisfy > their need for numbers? I've done a kernel build on x86_64 and if anything that > was slightly faster with these patches, but it was well within the noise > levels so it might be heat noise I'm looking at ;-)
Is it because you're reducing the number of TLB flushes, or what (kbuild isn't multi threaded so on x86 TLB flushes should be really fast anyway).
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