[libvirt] [RFC PATCH] libvirt support to force convergence of live guest migration

[Chegu Vinod]

On 11/26/2013 4:24 AM, Jiri Denemark wrote:
> On Thu, Nov 21, 2013 at 17:47:24 -0800, Chegu Vinod wrote:
>> Busy enterprise workloads hosted on large sized VM's tend to dirty
>> memory faster than the transfer rate achieved via live guest migration.
>> Despite some good recent improvements (& using dedicated 10Gig NICs
>> between hosts) the live migration may NOT converge.
>>
>> Recently support was added in qemu (version 1.6) to allow a user to
>> choose if they wish to force convergence of their migration via a
>> new migration capability : "auto-converge". This feature allows for qemu
>> to auto-detect lack of convergence and trigger a throttle-down of the
>> VCPUs.
>>
>> This RFC patch includes the libvirt support needed to trigger this
>> feature. (Testing is still in progress)
>>
>> Signed-off-by:  Chegu Vinod <chegu_vinod at hp.com>
>> ---
>>   include/libvirt/libvirt.h.in |    1 +
>>   src/qemu/qemu_migration.c    |   44 ++++++++++++++++++++++++++++++++++++++++++
>>   src/qemu/qemu_migration.h    |    1 +
>>   src/qemu/qemu_monitor.c      |    2 +-
>>   src/qemu/qemu_monitor.h      |    1 +
>>   tools/virsh-domain.c         |    7 ++++++
>>   6 files changed, 55 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
>> index 146a59b..13b0bfc 100644
>> --- a/include/libvirt/libvirt.h.in
>> +++ b/include/libvirt/libvirt.h.in
>> @@ -1192,6 +1192,7 @@ typedef enum {
>>       VIR_MIGRATE_OFFLINE           = (1 << 10), /* offline migrate */
>>       VIR_MIGRATE_COMPRESSED        = (1 << 11), /* compress data during migration */
>>       VIR_MIGRATE_ABORT_ON_ERROR    = (1 << 12), /* abort migration on I/O errors happened during migration */
>> +    VIR_MIGRATE_AUTO_CONVERGE     = (1 << 13), /* force auto-convergence during during migration */
>>   } virDomainMigrateFlags;
> I feel like there must be a better name we could use for this flag but
> I'm not able to come up with one... :-)
>
>> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
>> index e87ea85..8cc0c56 100644
>> --- a/src/qemu/qemu_migration.c
>> +++ b/src/qemu/qemu_migration.c
>> @@ -1565,6 +1565,40 @@ cleanup:
>>   }
>>   
>>   static int
>> +qemuMigrationSetAutoConverge(virQEMUDriverPtr driver,
>> +                            virDomainObjPtr vm,
>> +                            enum qemuDomainAsyncJob job)
> Nicely copied&pasted from qemuMigrationSetCompression but you forgot to
> fix indentation :-)
Yes being very new to libvirt...I did "leverage" from the previous 
changes :)
'will fix the indentation.

>> +{
>> +    qemuDomainObjPrivatePtr priv = vm->privateData;
>> +    int ret;
>> +
>> +    if (qemuDomainObjEnterMonitorAsync(driver, vm, job) < 0)
>> +        return -1;
>> +
>> +    ret = qemuMonitorGetMigrationCapability(
>> +                priv->mon,
>> +                QEMU_MONITOR_MIGRATION_CAPS_AUTO_CONVERGE);
>> +
>> +    if (ret < 0) {
>> +        goto cleanup;
>> +    } else if (ret == 0) {
>> +            virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
>> +                           _("Auto-Converge migration is not supported by "
>> +                             "QEMU binary"));
> Reduce indentation by one level. Also I think "migration" is not really
> needed in the error message, I'd just change it to
> "Auto-converge is not supported by QEMU binary".

Ok got it.

>
>> +        ret = -1;
>> +        goto cleanup;
>> +    }
>> +
>> +    ret = qemuMonitorSetMigrationCapability(
>> +                priv->mon,
>> +                QEMU_MONITOR_MIGRATION_CAPS_AUTO_CONVERGE);
>> +
>> +cleanup:
>> +    qemuDomainObjExitMonitor(driver, vm);
>> +    return ret;
>> +}
>> +
>> +static int
>>   qemuMigrationWaitForSpice(virQEMUDriverPtr driver,
>>                             virDomainObjPtr vm)
>>   {
>> @@ -2389,6 +2423,11 @@ qemuMigrationPrepareAny(virQEMUDriverPtr driver,
>>                                       QEMU_ASYNC_JOB_MIGRATION_IN) < 0)
>>           goto stop;
>>   
>> +    if (flags & VIR_MIGRATE_AUTO_CONVERGE &&
>> +        qemuMigrationSetAutoConverge(driver, vm,
>> +                                    QEMU_ASYNC_JOB_MIGRATION_IN) < 0)
>> +        goto stop;
>> +
> Hmm, I know you are just following what I did with
> VIR_MIGRATE_COMPRESSED, but setting auto-converge on destination doesn't
> make any sense. And it doesn't even make a lot of sense to set
> compression on destination (other than checking the destination supports
> compression) so I'm wondering why I did so.
>
>>       if (mig->lockState) {
>>           VIR_DEBUG("Received lockstate %s", mig->lockState);
>>           VIR_FREE(priv->lockState);
>> @@ -3181,6 +3220,11 @@ qemuMigrationRun(virQEMUDriverPtr driver,
>>                                       QEMU_ASYNC_JOB_MIGRATION_OUT) < 0)
>>           goto cleanup;
>>   
>> +    if (flags & VIR_MIGRATE_AUTO_CONVERGE &&
>> +        qemuMigrationSetAutoConverge(driver, vm,
>> +                                    QEMU_ASYNC_JOB_MIGRATION_OUT) < 0)
> Indentation is off by one space.
Ok
>> +        goto cleanup;
>> +
>>       if (qemuDomainObjEnterMonitorAsync(driver, vm,
>>                                          QEMU_ASYNC_JOB_MIGRATION_OUT) < 0)
>>           goto cleanup;
> ...
>
> So except for the small issues, the patch looks good to me. However, do
> I remember correctly that this feature can be turned on dynamically for
> an already running migration? If so, I think we want a second patch
> adding a new API for setting this auto-converge feature.

Yes.

Is there a sample reference/example that I could look up ?

Thanks for your feedback.
Vinod
> Jirka
> .
>