Best way to "renice" a process by name?

[Giorgos Keramidas]

On 2006-09-26 09:32, Brett Glass <brett at lariat.net> wrote:
> I'm working with a machine that's operating as a NAT router and
> recursive DNS resolver and is also running the Squid disk cache.
> Squid, in turn, spawns the "diskd" daemon, which does disk accesses on
> behalf of Squid. When Squid spawns diskd, it gives it a priority level
> 6 greater than itself. In other words, if Squid is launched normally,
> it gets a priority of 2 (normal) while diskd gets a priority of -4
> (very high).
>
> Unfortunately, diskd is not an efficient user of CPU (it seems to be
> polling for I/O completion) and is starving other processes on the
> machine (for example, natd) which need to operate in near real time.
>
> I'd like to keep diskd running on that machine, because having disk
> access done by a separate process is very efficient -- even more so if
> the system uses SMP. But I need to re-prioritize Squid and diskd to
> keep the rest of the machine functional. In particular, I'd like to
> nice Squid down by 1 (so that natd and named have priority over it)
> and have diskd run at standard priority (so that it can't starve other
> processes). This will keep diskd at a higher priority than Squid
> itself, which in turn will hopefully prevent message queues from
> overflowing.
>
> Reducing Squid's priority is simple; I can just edit the script that
> starts Squid so that /usr/bin/nice is used to invoke it. But taming
> diskd is more difficult, because diskd is a child process of Squid. I
> have to make sure it has started (which may require a delay loop),
> find out its PID, and then "renice" it by whatever increment is
> required to get it to the system's standard priority (2 by
> convention). Is there a "renice by name" utility for FreeBSD (sort of
> an equivalent of "killall")? I could gin one up, but since this seems
> like something that people would want to do frequently, find it hard
> to believe that someone hasn't already written one.

Maybe something like this helps?

    $ echo renice -n +10 -p `echo \`pgrep httpd\` | sed -e 's/ /,/g'`
    renice -n +10 -p 1023,656,655,654,653,652,610
    $

There is always a fair chance you might attempt to renice a process
which just happened to die, but this should be ok, unless you start
seeing PIDs being recycled too fast :)