Re: [lvm-devel] Re: 2x Oracle slowdown from 2.2.16 to 2.4.4

[Andi Kleen]

On Thu, Jul 12, 2001 at 04:30:46AM +0200, Andrea Arcangeli wrote:
> I will soon somehow make those changes in the lvm (based on beta7) in my
> tree and it will be interesting to see if this will make a difference. I
> will also have a look to see if I can improve a little more the lvm_map
> but other than those non rw semaphores there should be not a significant
> overhead to remove in the lvm fast path.

Even if you fix the snapshot_sem you still have the down on the _pe_lock 
in lvm_map. The part covered by the PE lock is only a few tenths of cycles
shorter than the part covered by the snapshot semaphore; so it is unlikely
that you see much difference unless you change both to rwsems.

Wouldn't a single semaphore be enough BTW to cover both? 

-Andi