Re: [PATCH 0/2] convert mmap_sem to a scalable rw_mutex

[Eric Dumazet]

Esben Nielsen a écrit :
> On Sat, 12 May 2007, Peter Zijlstra wrote:
>
> > On Sat, 2007-05-12 at 11:27 +0200, Esben Nielsen wrote:
> > > On Fri, 11 May 2007, Peter Zijlstra wrote:
> > >
> > > > I was toying with a scalable rw_mutex and found that it gives ~10% 
> > > > reduction in
> > > > system time on ebizzy runs (without the MADV_FREE patch).
> > >
> > > You break priority enheritance on user space futexes! :-(
> > > The problems is that the futex waiter have to take the mmap_sem. And as
> > > your rw_mutex isn't PI enabled you get priority inversions :-(
> >
> > Do note that rwsems have no PI either.
> > PI is not a concern for mainline - yet, I do have ideas here though.
> If PI wasn't a concern for mainline, why is PI futexes merged into the 
> mainline?

If you really care about futexes and mmap_sem, just use private futexes, since 
they dont use mmap_sem at all.


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