Date: Fri, 17 Mar 2000 09:38:13 +0100 (MET) From: Mats Lofkvist <mal@algonet.se> To: york@mediarack.com Cc: freebsd-smp@freebsd.org Subject: Re: *sigh* Message-ID: <200003170838.JAA22609@kairos.algonet.se> In-Reply-To: <000701bf8f9f$2b2859e0$5c5aca83@csd.unb.ca.acscience.com> (york@mediarack.com) References: <000701bf8f9f$2b2859e0$5c5aca83@csd.unb.ca.acscience.com>
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It has come to my attention that even with FreeBSD 3.3-RELEASE
SMP support, I do not see two processes marked runnable at any
given time.
Since concurrent execution of _processes_ on different cpu's has
worked since 3.0, there must either be something wrong in your setup,
or the way you check it.
One easy way to check if basic SMP works is to run two cpu-hogging
processes at the same time and check with top that both of them
get close to 100% cpu. (Note that 'RUN' in top doesn't mean
running, it means runnable. 'CPUN' means it is running on cpu N.)
My processors are both Intel (P3) and my motherboard is well
supported (ASUS).
It is my understanding that SMP support is not just to allow ping
ponging of processes between multiple CPU's for tasking
purposes, but to allow more than one concurrently running thread
and or process on seperate CPU's.
The support for executing separate threads in the same process on
different CPU's is still not quite there. There is a port of
the linux threads library to get that functionality, though.
I have worked with many SMP-supporting OS's such as Linux (ugh),
Solaris, Solaris X86 etc... All of which show more than one process
marked as runnable at any given time, and yet I see only a single
process marked runnable on this FreeBSD machine at any given
point. Whats more, benchmarks and other information from MySQL
show that threads are not executing concurrently accross the dual
CPU architecture which I have.
I'm quite sure I have the kernel options configured correctly, which is
why Im so confused about this.
Do you get the 'launching cpu 1' message at boot?
So, without further ado, I ask a simple question, does FreeBSD 4.0-R
fix this problem? Or is there some way I can fix it with 3.3-R such that
the SMP is working properly and or most efficiently, and allowing
threads to span CPU's and execute concurrently, and likewise with
processes?
AFAIK, the parallel scheduling of threads without the linux threads
library port is under development. The reason it isn't done yet is
(as always with FreeBSD :-) that it is being done the 'right way'
with a hybrid between user level and kernel threads, more like in
solaris than the 'all threads are kernel threads' solution in linux.
The reason you don't want kernel threads only is that for an application
that is not cpu-bound, the overhead of kernel threads is decreasing
application performance. E.g. if you check the volano java benchmarks
you can see that all linux numbers are with the java 'green threads'
library and not with the linux (kernel) threads library.
Thank you for your time.
-- Brent York
york@mediarack.com
_
Mats Lofkvist
mal@algonet.se
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