Re: open-scale-2.6.2-A0

[Ingo Molnar]

* Jamie Lokier <jamie@xxxxxxxxxxxxx> wrote:

> Ingo Molnar wrote:
> > i've attached an obvious scalability improvement for write()s. We in
> > essence used a system-global lock for every open(WRITE) - argh!
> 
> I wonder if the "rip the second arsehole" is there for a reason.

these days i dont think the comment is justified.

> Does this scalability improvement make any measured difference in any
> conceivable application, or is it just making struct inode larger?

i've not added any new lock, i'm merely reusing the existing ->i_lock. 
So there's no data or code bloat whatsoever.

one doesnt need any measurements to tell that a global cacheline
dirtying for every (most of the time completely unrelated) open(WRITE)
will hurt workloads that do that, especially on NUMA systems. I'd not be
surprised if it showed up in dbench/netbench.

	Ingo
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