Re: [Qemu-devel] [PATCH v3] Replace qemu_system_cond with VCPU stop mechanism

[Anthony Liguori <aliguori@us.ibm.com>]

On 08/22/2011 11:35 AM, Jan Kiszka wrote:
> On 2011-08-22 18:18, Avi Kivity wrote:
>> On 08/22/2011 06:46 PM, Jan Kiszka wrote:
>>> We can express the VCPU thread wakeup with the stop mechanism, saving
>>> both qemu_system_ready and the qemu_system_cond. For KVM threads, we can
>>> just enter the main loop as long as the thread is stopped. The central
>>> TCG thread is better held back before the loop as there can be side
>>> effects of the services called even when all CPUs are stopped.
>>>
>>> Creating VCPUs in stopped state will also be required for proper CPU
>>> hotplugging support.
>>>
>>>
>>> -    /* and wait for machine initialization */
>>> -    while (!qemu_system_ready) {
>>> -        qemu_cond_wait(&qemu_system_cond,&qemu_global_mutex);
>>> +    /* wait for initial kick-off after machine start */
>>> +    while (!first_cpu->stopped) {
>>> +        qemu_cond_wait(tcg_halt_cond,&qemu_global_mutex);
>>>        }
>>
>> Seems inverted - do we want to wait until first_cpu is stopped, or while
>> first_cpu is stopped?
>
> Oops, fixed below.
>
>>
>> Do we want to process run_on_cpu() events after the machine is created
>> but before a cpu is started (if starting with -S)?
>
> -S affects vm_running, not stopped states of individual VCPUs. So they
> will get kicked off on main_loop entry, but then stop again due to
> vm_running == 0.
>
> Jan
>
> -------8<--------
>
> We can express the VCPU thread wakeup with the stop mechanism, saving
> both qemu_system_ready and the qemu_system_cond. For KVM threads, we can
> just enter the main loop as long as the thread is stopped. The central
> TCG thread is better held back before the loop as there can be side
> effects of the services called even when all CPUs are stopped.
>
> Creating VCPUs in stopped state will also be required for proper CPU
> hotplugging support.
>
> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>

Applied.  Thanks.

Regards,

Anthony Liguori