Re: [Qemu-devel] [RFC PATCH v1 03/10] cpu: Reclaim vCPU objects

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Mon, Mar 07, 2016 at 08:05:58PM +0100, Thomas Huth wrote:
> On 04.03.2016 07:54, 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()
> >                 - Use iothread mutex instead of global mutex during
> >                   destroy
> >                 - Don't cleanup vCPU object from vCPU thread context
> >                   but leave it to the callers (device_add/device_del)]
> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  cpus.c               | 38 +++++++++++++++++++++++++++++++++++
> >  include/qom/cpu.h    | 10 +++++++++
> >  include/sysemu/kvm.h |  1 +
> >  kvm-all.c            | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> >  kvm-stub.c           |  5 +++++
> >  5 files changed, 110 insertions(+), 1 deletion(-)
> > 
> > diff --git a/cpus.c b/cpus.c
> > index 9592163..07cc054 100644
> > --- a/cpus.c
> > +++ b/cpus.c
> > @@ -953,6 +953,18 @@ 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");
> > +        exit(EXIT_FAILURE);
> > +    }
> > +}
> > +
> > +static void qemu_tcg_destroy_vcpu(CPUState *cpu)
> > +{
> > +}
> > +
> >  static void flush_queued_work(CPUState *cpu)
> >  {
> >      struct qemu_work_item *wi;
> > @@ -1053,6 +1065,11 @@ 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_iothread();
> > +            return NULL;
> > +        }
> 
> My comment from last time still applies:
> 
> You could increase readability of the code by changing the condition of
> the loop instead - currently it is a "while (1)" ... you could turn that
> into a "do { ... } while (!cpu->exit || cpu_can_run(cpu))" and then
> destroy the cpu after the loop.

Sorry for missing this, will take of this and the other comment in this
thread in the next version.

Regards,
Bharata.