Re: Support for SIGSTOP/SIGCONT in nice?

[Bob Proulx]

Jim Meyering wrote:
> Simon Josefsson wrote:
> > Frequently when I want to run a long-running I/O-bound job (i.e.,
> > rsync of the entire disk to a second disk) on a busy machine (i.e.,
> > mail and web server), the load increases to ~10 from a normal <1.
> > Using 'nice' doesn't help.  I don't know why this is, but I suspect
> > the kernel scheduler is sub-optimal for disk-bound jobs.
> >
> > Would it be useful to consider extending nice so it can send SIGSTOP
> > and SIGCONT signals in configurable intervals?  Having rsync run for
> > 30 seconds, sleep for 15, run for 30 seconds, etc, seem to avoid
> > slowing down the system to unusable levels.
> 
> Have you already tried using rsync's existing option to limit bandwidth?
>   rsync --bwlimit=500 ...

While doing some research into this problem I found that this
issue has been reported to rsync before.  Here is a previous thread
discussing it.

  http://lists.samba.org/archive/rsync/2004-February/008638.html

In the thread is an interesting perl snippet specifically for this
purpose.  It monitors load and stops and starts rsync as needed.

  http://lists.samba.org/archive/rsync/2004-February/008649.html

I would be inclined to see if the poster involved there made any
additional progress into this issue with rsync.  It has been two years
and so perhaps they found a good way to deal with this problem
already.

I was sure I have seen a generic script program that would cycle
another program on and off with sigstop/sigcont just as you are asking
for as a programmable load controller.  But it slips my mind at the
moment.  I did not find the one I was remembering.  [Any else have any
suggestions?]  But I did find something that seemed interesting so I
will include a pointer to it.

  http://www.pattosoft.com.au/jason/idleize/

Bob