From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [RFC][PATCH] Scheduler interface changes for credit2 Date: Mon, 22 Feb 2010 15:22:03 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com Cc: Keir Fraser List-Id: xen-devel@lists.xenproject.org Keir, any thoughts? Does this seem like a reasonable approach? Thanks, -George On Mon, Feb 15, 2010 at 5:20 PM, George Dunlap wrote: > The two attached patches change the scheduler interface to allow > credit2 to have several cpus share the same runqueue. =A0The patches > should have almost no impact on the current schedulers. =A0The patches > and their reasonings are below. =A0I'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. =A0This 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. =A0Furthermore, the > scheduler needs runqueues to be covered by a lock as well. =A0The > 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. =A0As 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 >