Re: cgroup management daemon

["Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>]

Quoting Tim Hockin (thockin-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org):
> What are the requirements/goals around performance and concurrency?
> Do you expect this to be a single-threaded thing, or can we handle
> some number of concurrent operations?  Do you expect to use threads of
> processes?

The cgmanager should be pretty dumb, so I would expect it to be
quite fast.  I don't have any specific perf goals though.  If you
have requirements I'm very interested to hear them.  I should be
able to tell pretty soon how far short I fall.

By default I'd expect to run with a single thread, but I don't
imagine one thread can serve a busy 1024-cpu system very well.
Unless you have guidance right now, I think I'd like to get
started with the basic functionality and see how it measures
up to your requirements.  I should add perf counters from the
start so we can figure out where bottlenecks (if any) are and
how to handle them.

Otherwise I could start out with a basic numcpus/10 threadpool
and have the main thread do socket i/o and parcel access
verification and vfs work out to the threadpool, but I'd rather
first know where the problems lie.

> Can you talk about logging - what and where?

When started under upstart, anything we print out goes to
/var/log/upstart/cgmanager.log.  Would be nice to keep it
that simple.  We could log requests by r to do something
it is not allowed to do, but it seems to me the failed
attempts cause no harm, while the potential for overflowing
logs can.

Did you have anything in mind?  Did you want logging to help
detect certain conditions for system optimization, or just
for failure notices and security violations?

> How will we handle event_fd?  Pass a file-descriptor back to the caller?

The only thing currently supporting eventfd is memory threshold,
right?  I haven't tested whether this will work or not, but
ideally the caller would open the eventfd fd, pass it, the
cgroup name, controller file to be watched, and the args to
cgmanager;  cgmanager confirms read access, opens the
controller fd, makes the request over cgroup.event_control,
then passes the controller fd back to the caller and closes
its own copy.

I'm also not sure whether the cgroup interface is going to be
offering a new feature to replace eventfd, since it wants
people to stop using cgroupfs...  Tejun?

> That's all I can come up with for now.

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