On 2015年01月14日 08:26, Al Stone wrote:
On 01/13/2015 10:22 AM, Grant Likely wrote:
On Mon, Jan 12, 2015 at 7:40 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
On Monday 12 January 2015 12:00:31 Grant Likely wrote:
On Mon, Jan 12, 2015 at 10:21 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
On Saturday 10 January 2015 14:44:02 Grant Likely wrote:
On Wed, Dec 17, 2014 at 10:26 PM, Grant Likely <grant.likely@xxxxxxxxxx> wrote:
This seems like a great fit for AML indeed, but I wonder what exactly
we want to hotplug here, since everything I can think of wouldn't need
AML support for the specific use case of SBSA compliant servers:
[...]
I've trimmed the specific examples here because I think that misses
the point. The point is that regardless of interface (either ACPI or
DT) there are always going to be cases where the data needs to change
at runtime. Not all platforms will need to change the CPU data, but
some will (say for a machine that detects a failed CPU and removes
it). Some PCI add-in boards will carry along with them additional data
that needs to be inserted into the ACPI namespace or DT. Some
platforms will have system level component (ie. non-PCI) that may not
always be accessible.
Just to be sure I get this right: do you mean runtime or boot-time
(re-)configuration for those?
Both are important.
ACPI has an interface baked in already for tying data changes to
events. DT currently needs platform specific support (which we can
improve on). I'm not even trying to argue for ACPI over DT in this
section, but I included it this document because it is one of the
reasons often given for choosing ACPI and I felt it required a more
nuanced discussion.
I can definitely see the need for an architected interface for
dynamic reconfiguration in cases like this, and I think the ACPI
model actually does this better than the IBM Power hypervisor
model, I just didn't see the need on servers as opposed to something
like a laptop docking station to give a more obvious example I know
from x86.
I know of at least one server product (non-ARM) that uses the
hot-plugging of CPUs and memory as a key feature, using the
ACPI OSPM model. Essentially, the customer buys a system with
a number of slots and pays for filling one or more of them up
front. As the need for capacity increases, CPUs and/or RAM gets
enabled; i.e., you have spare capacity that you buy as you need
it. If you use up all the CPUs and RAM you have, you buy more
cards, fill the additional slots, and turn on what you need. This
is very akin to the virtual machine model, but done with real hardware
instead.
There is another important user case for RAS, systems running critical
missions such as bank billing system, system like that need high
reliability that the machine can't be stopped.
So when error happened on hardware including CPU/memory DIMM on such
machines, we need to replace them at run-time.
Whether or not this product is still being sold, I do not know. I
have not worked for that company for eight years, and they were just
coming out as I left. Regardless, this sort of hot-plug does make
sense in the server world, and has been used in shipping products.
I think it still will be, Linux developers put lots of effort to
enable memory hotplug and computer node hotplug in the kernel [1], and
the code already merged into mainline.
[1]:
http://events.linuxfoundation.org/sites/events/files/lcjp13_chen.pdf
Thanks
Hanjun
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