On 23.04.2015 11:32, Peter Krempa wrote:
On Thu, Apr 23, 2015 at 11:19:34 +0200, Michal Privoznik wrote:
On 23.04.2015 10:30, Peter Krempa wrote:
On Thu, Apr 23, 2015 at 11:44:49 +0800, zhang bo wrote:
The function qemuBuildCommandLine() may take a long time, for example if we configure tens of vifs for the guest, each may cost hundrands of milliseconds to create tap dev, senconds in total. Thus, unlock vm before calling it.
Signed-off-by: Zhang Bo <oscar.zhangbo@huawei.com> Signed-off-by: Zhou Yimin <zhouyimin@huawei.com> --- src/qemu/qemu_process.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index 753afe8..d1aaaec 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -4628,14 +4628,18 @@ int qemuProcessStart(virConnectPtr conn, }
VIR_DEBUG("Building emulator command line"); + virObjectUnlock(vm); if (!(cmd = qemuBuildCommandLine(conn, driver, vm->def, priv->monConfig, priv->monJSON, priv->qemuCaps, migrateFrom, stdin_fd, snapshot, vmop, &buildCommandLineCallbacks, false, qemuCheckFips(), priv->autoNodeset, - &nnicindexes, &nicindexes))) + &nnicindexes, &nicindexes))) { + virObjectLock(vm); goto cleanup; + } + virObjectLock(vm);
Why do you need to unlock the object? The VM is starting at this point so you won't be able to save any time since APIs will either be blocked by a job or by the fact that the VM was not started.
Not true. We still allow QUERY jobs, or APIs that lock a domain object but don't necessarily take a job. For instance, if in one thread I'm doing virDomainGetOSType(), virDomainGetInfo(), ... (essentially 'virsh dominfo') while the other just starts the domain. I don't see a reason why virDomainGetOSType() should wait for the domain to be started up. Domain state should have no affect on the guest OS type, should it?
OK that is technically right. I wanted to point out that most of the stats are available only for online machines or it shouldn't be much of a problem to dealy the delivery.
Your example certainly doesn't illustrate why the delay to format the command line should be a problem when using libvirt. Or are you polling virDomainGetOSType every millisecond?
I am curious to see why the delay would be a problem.
Yep, I'm too. So far we don't really care much about libvirt response time (otherwise our critical sections would be much shorter), but maybe it's an issue for somebody.
On the other hand, I don't think we can just lock and unlock the domain object as we please. qemuBuildCommandLine is a very complex function and as such it calls many others. Some of them may rely on the fact, that the object is locked by caller.
Well, you definitely can't since almost everything in there is accessing vm->def. Locking semantics would be broken right in the line after @vm was unlocked by dereferencing it.
Well, anything that would change a domain definition should grap a MODIFY job. But such jobs are serialized, so even if we unlock the domain we should be okay to still access vm->def. What I am more worried about are all the small functions that interact with system or something. Currently they are serialized by @vm lock, but one we remove it ... Michal