Re: [RFC][PATCH] Scheduler interface changes for credit2

[George Dunlap <George.Dunlap@eu.citrix.com>]

Keir, any thoughts?  Does this seem like a reasonable approach?

Thanks,
 -George

On Mon, Feb 15, 2010 at 5:20 PM, George Dunlap
<George.Dunlap@eu.citrix.com> wrote:
> The two attached patches change the scheduler interface to allow
> credit2 to have several cpus share the same runqueue.  The patches
> should have almost no impact on the current schedulers.  The patches
> and their reasonings are below.  I've also attached the patches for
> the prototype credit2 scheduler, for reference.
>
> * Add a context swich callback (sched-context_switch-callback.diff)
>
> Add a callback to tell a scheduler that a vcpu has been completely
> context-switched off a cpu.
>
> When sharing a runqueue, we can't put a scheduled-out vcpu back on the
> runqueue until it's been completely de-scheduled, because it may be
> grabbed by another processor before it's ready.  This callback allows
> a scheduler to detect when a vcpu on its way out is completely off the
> processor, so that it can put the vcpu on the runqueue.
>
> * Allow sharing of locks between cpus (sched-spin_lock-pointers.diff)
>
> Have per-cpu pointers, initialized to per-cpu locks, which the
> scheduler may change during its init to reconfigure locking
> granularity.
>
> There are a number of race conditions having to do with updating of
> v->is_running and v->processor, all having to do with the fact that
> vcpus may change cpus without an explicit migrate.  Furthermore, the
> scheduler needs runqueues to be covered by a lock as well.  The
> cleanest way to solve all of these is to have the scheduler lock and
> the runqueue lock coincide.
>
> * Add a "scheduler" trace class (trace-sched-class.diff)
> Uses defined on a per-scheduler basis
>
> I've been running parallel kernel compiles on a 16-way box (2x4x2) for
> several hours now without deadlocks or BUG()s.  As far as I'm
> concerned, with these changes, credit2 is now ready to be checked in,
> as long as it's not set to the default scheduler.
>
> All of the above:
> Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
>