Yes. The nehalem processor has the integrated memory controller. But it
is not required that the hot-added memory should be onlined before
bringing up CPU.
I do the following memory-hotplug test on one Machine.
a. Before hot plugging memory, four CPUs socket are installed and
all the logical CPU are brought up. (Only one node has the memory)
b. The memory is hot-plugged and then the memory is onlined so that
it can be accessed by the system.
In the above testing case the CPU is brought up before onlining the
hot-added memory. And the test shows that it can work well.
That doesn't work when you have multiple nodes AFAICT. The cpus do not
come into service because of a lack of memory on the node.... per node
allocations will fail.
Just curious, exactly what did you test with? 2.6.33 (or newer)?
ie) with new processors it is possible that an entire node which
consists of memory and cpus comes and goes with the socket enable and
disable.
The cpu bringup code does local node allocations for the cpu. If the
memory connected to the node (which is "behind" the socket) isn't
online, then these allocations fail, and then the cpu bringup fails.
If the CPU can't allocate the memory from its own node, it can turn to
other node and see whether the memory can be allocated. And this depends
on the NUMA allocation policy.
Maybe that could work, but I haven't gotten that to work. Even if it
does work, it's a HUGE performance hit :(. I can't imagine incurring an
extra hop just to get to per_cpu memory. I'd rather bring the memory on
the local node up first.
I think it is much better to bring the memory up first.
Either way, it's a nice feature to have.
P.
P.
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