[libvirt] [PATCH 03/21] Convert QEMU driver mutex into a rwlock
Daniel P. Berrange
berrange at redhat.com
Wed Oct 28 17:52:17 UTC 2009
On Wed, Oct 28, 2009 at 05:24:00PM +0100, Daniel Veillard wrote:
> On Fri, Oct 23, 2009 at 02:05:32PM +0100, Daniel P. Berrange wrote:
> > A number of driver API methods which acquire the driver mutex
> > only ever used the driver object in a read-only fashion. All
> > these uses are converted to call qemuDriverLockRO() allowing
> > for greater concurrency.
> >
> > * src/qemu/qemu_conf.h: s/Mutex/RWLock/
> > * src/qemu/qemu_driver.c: Add a qemuDriverLockRO() method and use
> > it anywhere that doesn't require a write lock on the driver
>
> Hum, I still wonder about erro handling strategies there, for example
> even taking a read lock may fail not because of a programing error
> because there is already too many read lock taken.
>
> [...]
> > @@ -6834,6 +6846,8 @@ cleanup:
> >
> > if (vm)
> > virDomainObjUnlock(vm);
> > + qemuDriverUnlock(driver);
> > + qemuDriverLock(driver);
> > if (event)
> > qemuDomainEventQueue(driver, event);
> > qemuDriverUnlock(driver);
>
> Huh ??? really ? we need a way to allow other threads to get in ?
> Maybe a tiny wait here would allow a rescheduling especially if on a
> single processor.
This is a merge error.
> But otherwise this looks like a fairly automatic conversion so should
> go in with 02/21 when ready, ACK
I'm withdrawing this patch, and the one implementing RWLock. I believe I
have a more effective way to deal with concurrency. See the mail I just
sent out....
Daniel
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