Re: ufsstat - testers / feedback wanted!

In message: <20051014091004.GC18513_at_uk.tiscali.com>
            Brian Candler <B.Candler_at_pobox.com> writes:
: On Thu, Oct 13, 2005 at 11:10:26AM -0700, Brooks Davis wrote:
: > > I don't think you can measure one single interger (or 64bit) increase in face 
: > > of a operation that has to access backing store.  Even if there is a 
: > > performance hit, you don't have to build your kernel with the option enabled.
: > 
: > The one thing I'd be worried about here is that 64bit updates are
: > expensive on 32bit machines if you want them to be atomic.  Relative to
: > backing store they probably still don't matter, but the might be
: > noticable.
: 
: I'd be grateful if you could clarify that point for me. Are you saying that
: if I write
: 
:     long long foo;
:     ...
:     foo++;
: 
: then the C compiler generates code for 'foo++' which is not thread-safe?
: (And therefore I would have to protect it with a mutex or critical section)
: 
: Or are you saying that the C compiler inserts its own code around foo++ to
: turn it into a critical section, and therefore runs less efficiently than
: you'd expect?

You have to protect this thread-unsafe operation yourself.

Warner