Re: [Qemu-devel] [PATCH v5 04/10] cpu: Reclaim vCPU objects

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 11/20/2015 11:54 PM, Bharata B Rao wrote:
> From: Gu Zheng <guz.fnst@cn.fujitsu.com>
>
> In order to deal well with the kvm vcpus (which can not be removed without any
> protection), we do not close KVM vcpu fd, just record and mark it as stopped
> into a list, so that we can reuse it for the appending cpu hot-add request if
> possible. It is also the approach that kvm guys suggested:
> https://www.mail-archive.com/kvm@vger.kernel.org/msg102839.html
>
> Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> Signed-off-by: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
>                 [- Explicit CPU_REMOVE() from qemu_kvm/tcg_destroy_vcpu()
>                    isn't needed as it is done from cpu_exec_exit()]
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>   cpus.c               | 41 +++++++++++++++++++++++++++++++++++++
>   include/qom/cpu.h    | 10 +++++++++
>   include/sysemu/kvm.h |  1 +
>   kvm-all.c            | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>   kvm-stub.c           |  5 +++++
>   5 files changed, 113 insertions(+), 1 deletion(-)
>
> diff --git a/cpus.c b/cpus.c
> index 877bd70..af2b274 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -953,6 +953,21 @@ void async_run_on_cpu(CPUState *cpu, void (*func)(void *data), void *data)
>       qemu_cpu_kick(cpu);
>   }
>
> +static void qemu_kvm_destroy_vcpu(CPUState *cpu)
> +{
> +    if (kvm_destroy_vcpu(cpu) < 0) {
> +        error_report("kvm_destroy_vcpu failed.\n");
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    object_unparent(OBJECT(cpu));
> +}
> +
> +static void qemu_tcg_destroy_vcpu(CPUState *cpu)
> +{
> +    object_unparent(OBJECT(cpu));
> +}
> +
>   static void flush_queued_work(CPUState *cpu)
>   {
>       struct qemu_work_item *wi;
> @@ -1053,6 +1068,11 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
>               }
>           }
>           qemu_kvm_wait_io_event(cpu);
> +        if (cpu->exit && !cpu_can_run(cpu)) {
> +            qemu_kvm_destroy_vcpu(cpu);
> +            qemu_mutex_unlock(&qemu_global_mutex);


Nit: qemu_mutex_unlock_iothread() may be? Or it is important for 
iothread_locked to remain "true"? It does not seem to be used much though.



-- 
Alexey