On Mon, 26 Feb 2007 23:31:29 -0500, Rik van Riel <[EMAIL PROTECTED]> wrote:
> Hiro Yoshioka wrote: > > Hi, > > > > From: Rik van Riel <[EMAIL PROTECTED]> > >> 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? > > None. Each schedulable entity (whether a fully fledged > CPU core or an SMT/HT thread) is treated the same. > And what do the SMT and Multi-Core scheduling options in the kernel config are for ? Because of this thread I re-read the help text, and it looks like on could de-select the SMT scheduler option, get a working SMP system, and see what difference ? I suppose its related to migration and cache flushing and so on, but where could I get more details ? And more strange, what is the difference between multi-core and normal SMP configs ? > > 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? > > Not really, that would make it impossible for MySQL to > handle more simultaneous database queries than the system > has CPUs. > I don't know myqsl internals, but you assume one thread per query. If its more like Apache, one long living thread for several connections ? Its the same to answer 4+4 queries than 8 at half the speed, isn't it ? > Besides, it looks like this is not a problem in MySQL > per se (it works on FreeBSD) but some bug in Linux. > -- J.A. Magallon <jamagallon()ono!com> \ Software is like sex: \ It's better when it's free Mandriva Linux release 2007.1 (Cooker) for i586 Linux 2.6.19-jam07 (gcc 4.1.2 20070115 (prerelease) (4.1.2-0.20070115.1mdv2007.1)) #2 SMP PREEMPT - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/