Re: [BProc] priority control

[<er...@he...>]

On Thu, Mar 11, 2004 at 11:37:32PM +0900, Kimitoshi Takahashi wrote:
> Hello Erik,
> 
> I think it would be nice if the renice command on the master were correctly
> forwarded to slave nodes so that we are less dependent on queing systemes to prioritize jobs.
> What do you think ?

It's certainly a good thing to do.  It's an unintentional omission.
It's on the to-do list of things to fix but there's a lot of things on
that list.  I'm working on a port to Linux 2.6 in between helping out
with other stuff.

> I still can't understand why I couldn't bpsh renice, 
> since the PID on the slave was obtained  by "bpsh 1 ps -ef" and hence it should be local pid.  
> Would you elaborate a little more ?

When you do a ps on the slave node (via bpsh) you see the same process
IDs that the front end sees.  You'll note that a process doesn't
appear to change its PID when it moves to the back end.  The proc file
system is modified to show the pids that the front end sees.  This way
everything stays consistent when processes move around.  The slave
node has different process IDs internally but you don't see those.

You can see them if you turn off the PID mapping in /proc like this:

bpsh 1 -O /proc/sys/bproc/proc_pid_map echo 0

Putting a zero in that file turns off PID mapping.  1 means map for
non-root.  2 means map for everybody.  It defaults to 2.  If you turn
it off, then you get to see everything on the node.  You should be
able to see that the real pid is in that case.  If you use the real
pid, then I think renice should work.

> Anyway, I really like the bproc concept, and hope it will realize
> true light weight SSI.

Me too :)

- Erik