Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path

[Peter Zijlstra]

On Tue, Oct 01, 2013 at 09:48:02AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > On Sat, Sep 28, 2013 at 11:55:26AM -0700, Linus Torvalds wrote:
> > > So if the primary reason for this is really just that f*cking anon_vma
> > > lock, then I would seriously suggest:
> > 
> > I would still like to see the rwsem patches merged; even if we end up 
> > going back to a spin style anon_vma lock.
> > 
> > There's been various reports in the past about how programs are 
> > significantly faster if they wrap their mmap() calls in a pthread_mutex. 
> > And this was purely down to the fact that rwsem writer-writer contention 
> > blows chunks.
> 
> That's about the mm->mmap_sem rwsem, right?

Yep.

> That impact would have to be measured carefully, and not just for 
> workloads where we know that better contention logic helps, but other MM 
> workloads that are hitting hard on mmap_sem.

Sure.
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