linux-kernel - RE: [PATCH v4 0/6] ACPI: Add

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Date:	Wed, 30 May 2012 08:11:46 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"Moore, Robert" <robert.moore@...el.com>
Cc:	"shuahkhan@...il.com" <shuahkhan@...il.com>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"liuj97@...il.com" <liuj97@...il.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 0/6] ACPI: Add _OST support for ACPI hotplug

On Wed, 2012-05-30 at 02:56 +0000, Moore, Robert wrote:
> It does not make any difference. Essentially, a get_handle is performed by evaluate_object anyway.
> 

Thanks Robert for the confirmation!
-Toshi


> >-----Original Message-----
> >From: Toshi Kani [mailto:toshi.kani@...com]
> >Sent: Tuesday, May 29, 2012 4:43 PM
> >To: shuahkhan@...il.com
> >Cc: Moore, Robert; lenb@...nel.org; linux-acpi@...r.kernel.org;
> >bhelgaas@...gle.com; liuj97@...il.com; andi@...stfloor.org; linux-
> >kernel@...r.kernel.org
> >Subject: RE: [PATCH v4 0/6] ACPI: Add _OST support for ACPI hotplug
> >
> >On Tue, 2012-05-29 at 16:44 -0600, Shuah Khan wrote:
> >> On Tue, 2012-05-29 at 22:27 +0000, Moore, Robert wrote:
> >> > > > 2. Calling acpi_get_handle() on _OST prior to executing the method.
> >> > > > This will ensure that this method only gets run if it is present
> >> > > under
> >> > > > the device in question. Coupled with what is already outlined in #1
> >> > > > above, now _OST gets executed only when it is defined under the
> >> > > device object.
> >> > > > Example case in the existing code, please see
> >> > > acpi_processor_ppc_ost()
> >> > > > implementation.
> >> > >
> >> > > Yes, I did look at acpi_processor_ppc_ost() when I implemented the
> >> > > function.  I believe calling acpi_get_handle() is redundant since
> >> > > acpi_ns_get_node() is called within acpi_evaluate_object() as well.
> >> > > acpi_evaluate_object() simply returns with AE_NOT_FOUND when _OST
> >> > > method does not exist.
> >> > >
> >> >
> >> > This is correct. If _OST does not exist, AE_NOT_FOUND will be returned
> >from evaluate_object.
> >>
> >> Yes that is correct from the ACPI Spec and implementation point of view.
> >> My thinking is that a call to acpi_get_handle() might not penalize the
> >> OS as much as acpi_evaluate_object() would on systems that don't
> >> actually implement _OST. In other words, acpi_get_handle() might not go
> >> as deep as acpi_evaluate_object() would go into the ACPI layer, hence
> >> might be a safer measure on platforms that don't actually implement this
> >> optional method under all devices included in this patch set.
> >>
> >
> >I do not think we need to worry about it.  The code difference is not
> >that much, and this _OST path is limited to ACPI hotplug operations,
> >which are infrequent events.  Automatic workload balancing can make
> >frequent use of the operations, but is not frequent enough to make any
> >difference here.  I think simpler code works fine.
> >
> >Thanks,
> >-Toshi
> 


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