Subject: Re: CCL:Dual Xeon & G98

From: Bryan Putnam <bfp:at:purdue.edu>
Date: Fri, 7 Nov 2003 08:59:08 -0500 (EST)

On Tue, 4 Nov 2003, Close, David M. wrote:

> CCL'ers:
>   Someone told me I can run G98 jobs faster on my Dell 530 Workstation
> if IX use %Nproc=2 and make the following changes to the LINUX kernel
> for sharing memory.
>
> echo "67108864" >/proc/sys/kernel/shmmax
> echo "67108864" >/proc/sys/kernel/shmall
>
> only replace 67108864 with the amount of memory in your machine (in bytes)
>  Also, I know that the %Mem= should be per processor. Therefore, since I
> have 512Mb total memory and 2 processors, I should use something like
> %Mem=230Mb
>  Having done all this and also checking that the SMP kernel was running,
> I cannot get this to work. After only a second the program quits where
> the list of links to be used is printed.  The program ends with an
> "shmget failed" statement.  I presume this has something to do with
> shared memory, but I am not sure what to try next.  Perhaps someone
> knows what to try next, or perhaps what diagnostics to use to make sure
> the system has been configured properly.
>   Regards, Dave Close.
>
>
>

Here are some notes I received on this...
-Bryan

IF YOU WANT TO RUN SHARED-MEMORY ON AN SMP system.

Linux assumes that you want to share only small portions of memory, where
Gaussian wants big chunks. To allow larger chunks of memory to be shared,
add the following lines to /etc/sysctl.conf (requires reboot as this
forces a re-configure of the kernel at boot):

        kernel.shmmax=134217728
        kernel.shmall=134217728

(134217728 = 128*1024*1024 = 128Mb) You may set this according to your
memory needs. You are supposed to be able to write to the /proc/sys/kernel
files that control this on-the-fly, but it didn't seem to work for me and
would have to be done after each reboot anyway.