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    SubjectRe: [1/7,v8] NUMA Hotplug Emulator: documentation
    Shaohui,

    The documentation patch seems to be stale, it needs to be updated to match the
    new file names.

    On Tue, 07 Dec 2010, shaohui.zheng@intel.com wrote:

    > From: Shaohui Zheng <shaohui.zheng@intel.com>
    >
    > add a text file Documentation/x86/x86_64/numa_hotplug_emulator.txt
    > to explain the usage for the hotplug emulator.
    >
    > Reviewed-By: Randy Dunlap <randy.dunlap@oracle.com>
    > Signed-off-by: David Rientjes <rientjes@google.com>
    > Signed-off-by: Haicheng Li <haicheng.li@intel.com>
    > Signed-off-by: Shaohui Zheng <shaohui.zheng@intel.com>
    > ---
    > Index: linux-hpe4/Documentation/x86/x86_64/numa_hotplug_emulator.txt
    > ===================================================================
    > --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    > +++ linux-hpe4/Documentation/x86/x86_64/numa_hotplug_emulator.txt 2010-12-07 08:53:19.677622002 +0800
    > @@ -0,0 +1,102 @@
    > +NUMA Hotplug Emulator for x86_64
    > +---------------------------------------------------
    > +
    > +NUMA hotplug emulator is able to emulate NUMA Node Hotplug
    > +thru a pure software way. It intends to help people easily debug
    > +and test node/CPU/memory hotplug related stuff on a
    > +none-NUMA-hotplug-support machine, even a UMA machine and virtual
    > +environment.
    > +
    > +1) Node hotplug emulation:
    > +
    > +Adds a numa=possible=<N> command line option to set an additional N nodes
    > +as being possible for memory hotplug. This set of possible nodes
    > +control nr_node_ids and the sizes of several dynamically allocated node
    > +arrays.
    > +
    > +This allows memory hotplug to create new nodes for newly added memory
    > +rather than binding it to existing nodes.
    > +
    > +For emulation on x86, it would be possible to set aside memory for hotplugged
    > +nodes (say, anything above 2G) and to add an additional four nodes as being
    > +possible on boot with
    > +
    > + mem=2G numa=possible=4
    > +
    > +and then creating a new 128M node at runtime:
    > +
    > + # echo 128M@0x80000000 > /sys/kernel/debug/node/add_node
    > + On node 1 totalpages: 0
    > + init_memory_mapping: 0000000080000000-0000000088000000
    > + 0080000000 - 0088000000 page 2M
    > +
    > +Once the new node has been added, its memory can be onlined. If this
    > +memory represents memory section 16, for example:
    > +
    > + # echo online > /sys/devices/system/memory/memory16/state
    > + Built 2 zonelists in Node order, mobility grouping on. Total pages: 514846
    > + Policy zone: Normal
    > + [ The memory section(s) mapped to a particular node are visible via
    > + /sys/devices/system/node/node1, in this example. ]
    > +
    > +2) CPU hotplug emulation:
    > +
    > +The emulator reserves CPUs thru grub parameter, the reserved CPUs can be
    > +hot-add/hot-remove in software method, it emulates the process of physical
    > +cpu hotplug.
    > +
    > +When hotplugging a CPU with emulator, we are using a logical CPU to emulate the
    > +CPU socket hotplug process. For the CPU supported SMT, some logical CPUs are in
    > +the same socket, but it may located in different NUMA node after we have
    > +emulator. We put the logical CPU into a fake CPU socket, and assign it a
    > +unique phys_proc_id. For the fake socket, we put one logical CPU in only.
    > +
    > + - to hide CPUs
    > + - Using boot option "maxcpus=N" hide CPUs
    > + N is the number of CPUs to initialize; the reset will be hidden.
    > + - Using boot option "cpu_hpe=on" to enable CPU hotplug emulation
    > + when cpu_hpe is enabled, the rest CPUs will not be initialized
    > +
    > + - to hot-add CPU to node
    > + # echo nid > cpu/probe
    > +
    > + - to hot-remove CPU
    > + # echo nid > cpu/release
    > +
    > +3) Memory hotplug emulation:
    > +
    > +The emulator reserves memory before OS boots, the reserved memory region is
    > +removed from e820 table. Each online node has an add_memory interface, and
    > +memory can be hot-added via the per-ndoe add_memory debugfs interface.
    > +
    > +The difficulty of Memory Release is well-known, we have no plan for it until
    > +now.
    > +
    > + - reserve memory thru a kernel boot paramter
    > + mem=1024m
    > +
    > + - add a memory section to node 3
    > + # echo 0x40000000 > mem_hotplug/node3/add_memory
    > + OR
    > + # echo 1024m > mem_hotplug/node3/add_memory
    > +
    > +4) Script for hotplug testing
    > +
    > +These scripts provides convenience when we hot-add memory/cpu in batch.
    > +
    > +- Online all memory sections:
    > +for m in /sys/devices/system/memory/memory*;
    > +do
    > + echo online > $m/state;
    > +done
    > +
    > +- CPU Online:
    > +for c in /sys/devices/system/cpu/cpu*;
    > +do
    > + echo 1 > $c/online;
    > +done
    > +
    > +- David Rientjes <rientjes@google.com>
    > +- Haicheng Li <haicheng.li@intel.com>
    > +- Shaohui Zheng <shaohui.zheng@intel.com>
    > + Nov 2010
    >
    > --
    > Thanks & Regards,
    > Shaohui
    >
    >
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