Re: [PATCH 0/5][RFC] more fine grained locking for IRQ injection

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 13, 2009 at 04:28:09PM +0300, Gleb Natapov wrote:
> On Mon, Jul 13, 2009 at 04:23:36PM +0300, Michael S. Tsirkin wrote:
> > On Mon, Jul 13, 2009 at 12:12:30PM +0300, Gleb Natapov wrote:
> > > kvm->irq_lock protects too much stuff, but still fail to protect
> > > everything it was design to protect (see ack notifiers call in pic). I
> > > want to make IRQ injection logic use more fine grained locking.
> > 
> > At least irq routing changes and notifier list changes
> > do not seem to be involved in irq injection.
> > So why do we want fine-grained locking there?
> > 
> When you have one big lock and you want to eliminate it you look at all
> things it protects and you start introducing different locking for
> unrelated stuff. This is what this patch series does, so I don't really
> get you point.

But why do you want to eliminate it? What is the operation that this
will speed up? Is there a contention issue and which operations
contend on the lock?

> > > This patch
> > > series split kvm->irq_lock mutex to smaller spinlocks each one protects
> > > only one thing. Irq routing, irq notifier lists and ioapic gain their own
> > > spinlock.  pic is already uses its own lock. This patch series also makes
> > > interrupt injection to lapic lockless (several kvm_irq_delivery_to_apic()
> > > may run in parallel), but access to lapic was never fully locked in the
> > > first place. VCPU could access lapic in parallel with interrupt injection.
> > > 
> > > The patch series is on top of my previous series that converts ack notifiers
> > > to the RCU locking.
> > > 
> > > Gleb Natapov (5):
> > >   Protect irq_sources_bitmap by kvm->lock instead of kvm->irq_lock
> > >   Move irq routing to its own locking.
> > >   Move irq notifiers lists to its own locking.
> > >   Move IO APIC to its own lock.
> > >   Drop kvm->irq_lock lock.
> > > 
> > >  arch/ia64/kvm/kvm-ia64.c |   29 +++++++++++++++++++--------
> > >  arch/x86/kvm/i8254.c     |    4 +-
> > >  arch/x86/kvm/lapic.c     |    7 +-----
> > >  arch/x86/kvm/x86.c       |   32 +++++++++++++++++++-----------
> > >  include/linux/kvm_host.h |    3 +-
> > >  virt/kvm/eventfd.c       |    2 -
> > >  virt/kvm/ioapic.c        |   47 +++++++++++++++++++++++++++------------------
> > >  virt/kvm/ioapic.h        |    1 +
> > >  virt/kvm/irq_comm.c      |   35 ++++++++++++++-------------------
> > >  virt/kvm/kvm_main.c      |    7 ++---
> > >  10 files changed, 92 insertions(+), 75 deletions(-)
> > > 
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> 
> --
> 			Gleb.
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