Re: SMP performance degradation with sysbench

[Hiro Yoshioka <hyoshiok@miraclelinux.com>]

Hi,

From: Rik van Riel <riel@redhat.com>
> Hiro Yoshioka wrote:
> > Howdy,
> > 
> > MySQL 5.0.26 had some scalability issues and it solved since 5.0.32
> > http://ossipedia.ipa.go.jp/capacity/EV0612260303/
> > (written in Japanese but you may read the graph. We compared
> > 5.0.24 vs 5.0.32)
snip
> > MySQL tries to get a mutex but it spends about 16.8% of CPU on 8 core
> > machine.
> > 
> > I think there are a lot of room to be inproved in MySQL implementation.
> 
> That's one aspect.
> 
> The other aspect of the problem is that when the number of
> threads exceeds the number of CPU cores, Linux no longer
> manages to keep the CPUs busy and we get a lot of idle time.
> 
> On the other hand, with the number of threads being equal to
> the number of CPU cores, we are 100% CPU bound...

I have a question. If so, what is the difference of kernel's
view between SMP and CPU cores?

Another question. When the number of threads exceeds the number of
CPU cores, we may get a lot of idle time. Then a workaround of
MySQL is that do not creat threads which exceeds the number
of CPU cores. Is it right?

Regards,
  Hiro
--
Hiro Yoshioka
CTO/Miracle Linux Corporation
http://blog.miraclelinux.com/yume/