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From: Like Xu <like.xu@linux.intel.com>
Message-ID: <965d5d2f-1717-dcd0-8707-f6629f54e504@linux.intel.com>
Date: Tue, 2 Apr 2019 10:35:30 +0800
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Subject: Re: [Qemu-devel] [PATCH 4/9] cpu/topology: add ARM support for smp
 machine properties
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: qemu-trivial@nongnu.org, qemu-devel@nongnu.org, like.xu@intel.com, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>

On 2019/4/2 7:38, Eduardo Habkost wrote:
> On Mon, Apr 01, 2019 at 10:56:30AM +0800, Like Xu wrote:
>> On 2019/3/29 17:27, Alex Bennée wrote:
> [...]
>>>> @@ -1713,6 +1717,9 @@ static void cortex_a9_initfn(Object *obj)
>>>>    #ifndef CONFIG_USER_ONLY
>>>>    static uint64_t a15_l2ctlr_read(CPUARMState *env, const ARMCPRegInfo *ri)
>>>>    {
>>>> +    MachineState *ms = MACHINE(qdev_get_machine());
>>>
>>> How expensive is qdev_get_machine? This could potentially be a
>>> performance issue if this register is read a lot.
>>
>> It may not bother us cause the MachineState object would be feteched from
>> qemu QOM at its first requested time and save it as static variable for
>> incoming requests.
> 
> We already have a current_machine variable declared in
> include/hw/boards.h.  We normally avoid using it and use
> MACHINE(qdev_get_machine()) instead, but I never understood why.
>
Which one do you prefer to access smp machine properties?