Re: [Qemu-devel] [PATCH 4/9] cpu/topology: add ARM support for smp machine properties

From: Eduardo Habkost <ehabkost@redhat.com>
To: Like Xu <like.xu@linux.intel.com>
Cc: "Alex Bennée" <alex.bennee@linaro.org>,
	qemu-devel@nongnu.org, qemu-trivial@nongnu.org,
	like.xu@intel.com, "Igor Mammedov" <imammedo@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 4/9] cpu/topology: add ARM support for smp machine properties
Date: Mon, 1 Apr 2019 20:38:18 -0300	[thread overview]
Message-ID: <20190401233818.GA22884@habkost.net> (raw)
In-Reply-To: <2546bf3e-2009-5a76-bc63-0ad73d333a78@linux.intel.com>

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.

-- 
Eduardo