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vmm: cpu: Reuse already allocated vCPUs if available

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When a request is made to increase the number of vCPUs in the VM attempt
to reuse any previously removed (and hence inactive) vCPUs before
creating new ones.

This ensures that the APIC ID is not reused for a different KVM vCPU
(which is not allowed) and that the APIC IDs are also sequential.

The two key changes to support this are:

* Clearing the "kill" bit on the old vCPU state so that it does not
  immediately exit upon thread recreation.
* Using the length of the vcpus vector (the number of allocated vcpus)
  rather than the number of active vCPUs (.present_vcpus()) to determine
  how many should be created.

This change also introduced some new info!() debugging on the vCPU
creation/removal path to aid further development in the future.

TEST=Expanded test_cpu_hotplug test.

Fixes: #1338

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2020-06-23 12:52:17 +01:00
parent 9dcd0c37f3
commit 4b64f2a027
2 changed files with 18 additions and 1 deletions
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13
tests/integration.rs
View File

@ -3775,6 +3775,19 @@ mod tests {
u32::from(desired_vcpus)
);
// Resize the VM back up to 4
let desired_vcpus = 4;
resize_command(&api_socket, Some(desired_vcpus), None);
guest.ssh_command("echo 1 | sudo tee /sys/bus/cpu/devices/cpu2/online")?;
guest.ssh_command("echo 1 | sudo tee /sys/bus/cpu/devices/cpu3/online")?;
thread::sleep(std::time::Duration::new(10, 0));
aver_eq!(
tb,
guest.get_cpu_count().unwrap_or_default(),
u32::from(desired_vcpus)
);
let _ = child.kill();
let _ = child.wait();
Ok(())

6
vmm/src/cpu.rs
View File

@ -750,6 +750,7 @@ impl CpuManager {
Ok(vcpu_clone)
}
/// Only create new vCPUs if there aren't any inactive ones to reuse
fn create_vcpus(&mut self, desired_vcpus: u8, entry_point: Option<EntryPoint>) -> Result<()> {
info!(
"Request to create new vCPUs: desired = {}, max = {}, allocated = {}, present = {}",
@ -763,7 +764,8 @@ impl CpuManager {
return Err(Error::DesiredVCPUCountExceedsMax);
}
for cpu_id in self.present_vcpus()..desired_vcpus {
// Only create vCPUs in excess of all the allocated vCPUs.
for cpu_id in self.vcpus.len() as u8..desired_vcpus {
let vcpu = self.create_vcpu(cpu_id, entry_point, None)?;
self.vcpus.push(vcpu);
}
@ -859,6 +861,7 @@ impl CpuManager {
Ok(())
}
/// Start up as many vCPUs threads as needed to reach `desired_vcpus`
fn activate_vcpus(&mut self, desired_vcpus: u8, inserting: bool) -> Result<()> {
if desired_vcpus > self.config.max_vcpus {
return Err(Error::DesiredVCPUCountExceedsMax);
@ -875,6 +878,7 @@ impl CpuManager {
self.present_vcpus()
);
// This reuses any inactive vCPUs as well as any that were newly created
for cpu_id in self.present_vcpus()..desired_vcpus {
let vcpu = Arc::clone(&self.vcpus[cpu_id as usize]);
self.start_vcpu(vcpu, vcpu_thread_barrier.clone(), inserting)?;