linux-kernel - Re: [1/7,v8] NUMA Hotplug Emulator: documentation

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Date:	Tue, 7 Dec 2010 11:24:20 -0700
From:	Eric B Munson <emunson@...bm.net>
To:	shaohui.zheng@...el.com
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...ux.intel.com,
	shaohui.zheng@...ux.intel.com, rientjes@...gle.com,
	dave@...ux.vnet.ibm.com, gregkh@...e.de,
	Haicheng Li <haicheng.li@...el.com>
Subject: Re: [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@...el.com wrote:

> From: Shaohui Zheng <shaohui.zheng@...el.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@...cle.com>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> Signed-off-by: Haicheng Li <haicheng.li@...el.com>
> Signed-off-by: Shaohui Zheng <shaohui.zheng@...el.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@...0000000 > /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@...gle.com>
> +- Haicheng Li <haicheng.li@...el.com>
> +- Shaohui Zheng <shaohui.zheng@...el.com>
> +  Nov 2010
> 
> -- 
> Thanks & Regards,
> Shaohui
> 
> 
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