Re: [Qemu-devel] [PATCH V3] Guest stop notification

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-12-02 22:27, Eric B Munson wrote:
> On Fri, 02 Dec 2011, Jan Kiszka wrote:
> 
>> On 2011-12-02 20:19, Eric B Munson wrote:
>>> Often when a guest is stopped from the qemu console, it will report spurious
>>> soft lockup warnings on resume.  There are kernel patches being discussed that
>>> will give the host the ability to tell the guest that it is being stopped and
>>> should ignore the soft lockup warning that generates.
>>>
>>> Signed-off-by: Eric B Munson <emunson@mgebm.net>
>>> Cc: Avi Kivity <avi@redhat.com>
>>> Cc: Marcelo Tosatti <mtosatti@redhat.com>
>>> Cc: Jan Kiszka <jan.kiszka@siemens.com>
>>> Cc: ryanh@linux.vnet.ibm.com
>>> Cc: aliguori@us.ibm.com
>>> Cc: kvm@vger.kernel.org
>>>
>>> ---
>>> Changes from V2:
>>>  Move ioctl into hw/kvmclock.c so as other arches can use it as it is
>>> implemented
>>>
>>> Changes from V1:
>>>  Remove unnecessary encapsulating function
>>>
>>>  hw/kvmclock.c |   24 ++++++++++++++++++++++++
>>>  1 files changed, 24 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/hw/kvmclock.c b/hw/kvmclock.c
>>> index 5388bc4..756839f 100644
>>> --- a/hw/kvmclock.c
>>> +++ b/hw/kvmclock.c
>>> @@ -16,6 +16,7 @@
>>>  #include "sysbus.h"
>>>  #include "kvm.h"
>>>  #include "kvmclock.h"
>>> +#include "cpu-all.h"
>>>  
>>>  #include <linux/kvm.h>
>>>  #include <linux/kvm_para.h>
>>> @@ -69,11 +70,34 @@ static void kvmclock_vm_state_change(void *opaque, int running,
>>>      }
>>>  }
>>>  
>>> +static void kvmclock_vm_state_change_vcpu(void *opaque, int running,
>>> +                                          RunState state)
>>> +{
>>> +    int ret;
>>> +    CPUState *penv = first_cpu;
>>> +
>>> +    if (running) {
>>> +	while (penv) {
>>
>> or: for (cpu = first_cpu; cpu != NULL; cpu = cpu->next_cpu) {
>>
> 
> Functionally equivalent and I see both in the code, is there a standard?

Not really. I once tried to introduce an iterator macro, but it was
refused. The above is just more compact.

But this is only a minor nit.

> 
>>> +            ret = kvm_vcpu_ioctl(penv, KVM_GUEST_PAUSED, 0);
>>> +            if (ret) {
>>> +                if (ret != ENOSYS) {
>>> +                    fprintf(stderr,
>>> +                            "kvmclock_vm_state_change_vcpu: %s\n",
>>> +                            strerror(-ret));
>>> +                }
>>> +                return;
>>> +            }
>>> +            penv = (CPUState *)penv->next_cpu;
>>
>> Unneeded cast.
>>
> 
> Also following an example seen elsewhere.

Generally, we try to avoid those pointless casts.

> 
>>> +        }
>>> +    }
>>> +}
>>> +
>>
>> Again: please use checkpatch.pl.
>>
> 
> Sorry, tough to get used to hitting space bar that many times...
> 
>>>  static int kvmclock_init(SysBusDevice *dev)
>>>  {
>>>      KVMClockState *s = FROM_SYSBUS(KVMClockState, dev);
>>>  
>>>      qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
>>> +    qemu_add_vm_change_state_handler(kvmclock_vm_state_change_vcpu, NULL);
>>>      return 0;
>>>  }
>>>  
>>
>> Why not extend the existing handler?
> 
> Because the new handler doesn't touch the KVMClockState object.  If this is
> preferred, I have no objection.

The separate registration looks strange to me. And the fact that you
don't need to object doesn't justify a callback of its own.

> 
>>
>> I still wonder if the IOCTL interface is actually kvmclock specific. But
>> Marcello asked for this, and we could still change it when some arch
>> comes around that provides it independent of kvmclock.
> 
> The flag itself is stored in the pvclock_vcpu_time_info structure, and anything
> else that touches that structure uses ioctls.

That's the host-guest interface. But I'm talking about the kvm-qemu
interface here which has no relation to how the "was paused" information
is transferred to the guest.

Jan


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