Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

[Christoph Lameter]

On Fri, 8 Jan 2010, Linus Torvalds wrote:

> That's a huge jump. It's clear that the spinlock-based rwsem's simply
> suck.  The speculation gets rid of some additional mmap_sem contention,
> but at least for two sockets it looks like the rwsem implementation was
> the biggest problem by far.

I'd say that the ticket lock sucks for short critical sections vs. a
simple spinlock since it forces the cacheline into shared mode.

> Of course, larger numbers of sockets will likely change the situation, but
> at the same time I do suspect that workloads designed for hundreds of
> cores will need to try to behave better than that benchmark anyway ;)

Can we at least consider a typical standard business server, dual quad
core hyperthreaded with 16 "cpus"? Cacheline contention will increase
significantly there.

> Because let's face it - if your workload does several million page faults
> per second, you're just doing something fundamentally _wrong_.

You may just want to get your app running and its trying to initialize
its memory in parallel on all threads. Nothing wrong with that.

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