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

[Jan Kiszka]

On 2011-12-03 12:19, Marcelo Tosatti wrote:
> On Sat, Dec 03, 2011 at 10:06:56AM +0100, Jan Kiszka wrote:
>> 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 <address@hidden>
>>>>> Cc: Avi Kivity <address@hidden>
>>>>> Cc: Marcelo Tosatti <address@hidden>
>>>>> Cc: Jan Kiszka <address@hidden>
>>>>> Cc: address@hidden
>>>>> Cc: address@hidden
>>>>> Cc: address@hidden
>>>>>
>>>>> ---
>>>>> 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
> 
> It is one simple, rarely used command. I don't see why another interface
> such as kvm_run would be beneficial for this case.
> 

I was referring to the relation between the IOCTL and kvmclock, but
IOCTL vs. kvm_run.

Jan

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