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Re: [libvirt] [PATCH v3 4/6] qemu: Implement period and quota tunable XML configuration and parsing



At 07/19/2011 04:59 AM, Adam Litke Write:
> 
> 
> On 07/18/2011 04:42 AM, Wen Congyang wrote:
>> +int qemuSetupCgroupForVcpu(struct qemud_driver *driver, virDomainObjPtr vm)
>> +{
>> +    virCgroupPtr cgroup = NULL;
>> +    virCgroupPtr cgroup_vcpu = NULL;
>> +    qemuDomainObjPrivatePtr priv = vm->privateData;
>> +    int rc;
>> +    unsigned int i;
>> +    unsigned long long period = vm->def->cputune.period;
>> +    long long quota = vm->def->cputune.quota;
>> +
>> +    if (driver->cgroup == NULL)
>> +        return 0; /* Not supported, so claim success */
>> +
>> +    rc = virCgroupForDomain(driver->cgroup, vm->def->name, &cgroup, 0);
>> +    if (rc != 0) {
>> +        virReportSystemError(-rc,
>> +                             _("Unable to find cgroup for %s"),
>> +                             vm->def->name);
>> +        goto cleanup;
>> +    }
>> +
>> +    if (priv->nvcpupids == 0 || priv->vcpupids[0] == vm->pid) {
>> +        /* If we does not know VCPU<->PID mapping or all vcpu runs in the same
>> +         * thread, we can not control each vcpu.
>> +         */
>> +        if (period || quota) {
>> +            if (qemuCgroupControllerActive(driver, VIR_CGROUP_CONTROLLER_CPU)) {
>> +                if (qemuSetupCgroupVcpuBW(cgroup, period, quota) < 0)
>> +                    goto cleanup;
>> +            }
>> +        }
>> +        return 0;
>> +    }
> 
> I found a problem above.  In the case where we are controlling quota at
> the domain level cgroup we must multiply the user-specified quota by the
> number of vcpus in the domain in order to get the same performance as we
> would with per-vcpu cgroups.  As written, the vm will be essentially
> capped at 1 vcpu worth of quota regardless of the number of vcpus.  You
> will also have to apply this logic in reverse when reporting the
> scheduler statistics so that the quota number is a per-vcpu quantity.

When quota is 1000, and per-vcpu thread is not active, we can start
vm successfully. When the per-vcpu thread is active, and the num of
vcpu is more than 1, we can not start vm if we multiply the user-specified
quota. It will confuse the user: sometimes the vm can be started, but
sometimes the vm can not be started with the same configuration.

> 
> 


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