[Fwd: Re: Mysql - Linuxthreads : Still needed?]

[Daniel Eischen]

On Mon, 15 Nov 2004, Robert Watson wrote:

>
> On Wed, 10 Nov 2004, Julian Elischer wrote:
>
> > send to the right list.
>
> So, the good news is that we've successfully dramatically improved the
> performance of MySQL between 5.2 and 5.3.  The mixed news is that clearly
> we have more work to do. :-)  Out of curiousity, has anyone done much in
> the way of kernel profiling during heavy duty MySQL runs to see if there
> are specific kernel bottlenecks we can be working on?
>
> I've noticed that we're contending a fair amount on UNIX domain socket
> locking, although with Giant off the stack this is a big improvement over
> what we saw previously.  Although it was a few months ago, my recollection
> from profiling the mutex use and kernel use is that we're spending a lot
> of time checking to see if we have to deliver signals to threads or not in
> kernel.  I may have the opportunity to do a bit of profiling today or
> tomorrow and see what I bump into.

David did a bit of research and found that in M:N cases there
is a lot of contention for upcall allocation (actually I think
it is thread allocation) in the kernel.  It looks like we
completely teardown and free completed threads, then reallocate
and set them up again when they unblock and we need a new thread
to convert into an upcall.  It would probably be faster to cache
them (hang them off the KSE group) instead of completely tearing
them down and deallocating them.

-- 
Dan Eischen