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docs: update documentation for memory hot unplug

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Add specification about how to use memory hot unplug, and add
a flow diagram to explain memory hot unplug process.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Zhu Guihua 2015-04-27 16:47:15 +08:00 committed by Michael S. Tsirkin
parent 850d00700b
commit 4fccb4834d
2 changed files with 61 additions and 4 deletions
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23
docs/memory-hotplug.txt
View File

@ -4,9 +4,7 @@ QEMU memory hotplug
This document explains how to use the memory hotplug feature in QEMU, This document explains how to use the memory hotplug feature in QEMU,
which is present since v2.1.0. which is present since v2.1.0.
Please, note that memory hotunplug is not supported yet. This means Guest support is required for memory hotplug to work.
that you're able to add memory, but you're not able to remove it.
Also, proper guest support is required for memory hotplug to work.
Basic RAM hotplug Basic RAM hotplug
----------------- -----------------
@ -74,3 +72,22 @@ comes from regular RAM, 1GB is a 1GB hugepage page and 256MB is from
-device pc-dimm,id=dimm1,memdev=mem1 \ -device pc-dimm,id=dimm1,memdev=mem1 \
-object memory-backend-file,id=mem2,size=256M,mem-path=/mnt/hugepages-2MB \ -object memory-backend-file,id=mem2,size=256M,mem-path=/mnt/hugepages-2MB \
-device pc-dimm,id=dimm2,memdev=mem2 -device pc-dimm,id=dimm2,memdev=mem2
RAM hot-unplug
---------------
In order to be able to hot unplug pc-dimm device, QEMU has to be told the ids
of pc-dimm device and memory backend object. The ids were assigned when you hot
plugged memory.
Two monitor commands are used to hot unplug memory:
- "device_del": deletes a front-end pc-dimm device
- "object_del": deletes a memory backend object
For example, assuming that the pc-dimm device with id "dimm1" exists, and its memory
backend is "mem1", the following commands tries to remove it.
(qemu) device_del dimm1
(qemu) object_del mem1

42
docs/specs/acpi_mem_hotplug.txt
View File

@ -2,7 +2,7 @@ QEMU<->ACPI BIOS memory hotplug interface
-------------------------------------- --------------------------------------
ACPI BIOS GPE.3 handler is dedicated for notifying OS about memory hot-add ACPI BIOS GPE.3 handler is dedicated for notifying OS about memory hot-add
events. and hot-remove events.
Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access): Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access):
--------------------------------------------------------------- ---------------------------------------------------------------
@ -42,3 +42,43 @@ Selecting memory device slot beyond present range has no effect on platform:
ignored ignored
- read accesses to memory hot-plug registers not documented above return - read accesses to memory hot-plug registers not documented above return
all bits set to 1. all bits set to 1.
Memory hot remove process diagram:
----------------------------------
+-------------+     +-----------------------+      +------------------+     
 |  1. QEMU    |     | 2. QEMU               |      |3. QEMU           |     
 |  device_del +---->+ device unplug request +----->+Send SCI to guest,|     
 |             |     |         cb            |      |return control to |     
 +-------------+     +-----------------------+      |management        |     
                                                    +------------------+     
                                                                             
 +---------------------------------------------------------------------+     
                                                                             
 +---------------------+              +-------------------------+            
 | OSPM:               | remove event | OSPM:                   |            
 | send Eject Request, |              | Scan memory devices     |            
 | clear remove event  +<-------------+ for event flags         |            
 |                     |              |                         |            
 +---------------------+              +-------------------------+            
           |                                                                 
           |                                                                 
 +---------v--------+            +-----------------------+                   
 | Guest OS:        |  success   | OSPM:                 |                   
 | process Ejection +----------->+ Execute _EJ0 method,  |                   
 | request          |            | set eject bit in flags|                   
 +------------------+            +-----------------------+                   
           |failure                         |                                
           v                                v                                
 +------------------------+      +-----------------------+                   
 | OSPM:                  |      | QEMU:                 |                   
 | set OST event & status |      | call device unplug cb |                   
 | fields                 |      |                       |                   
 +------------------------+      +-----------------------+                   
          |                                  |                               
          v                                  v                               
 +------------------+              +-------------------+                     
 |QEMU:             |              |QEMU:              |                     
 |Send OST QMP event|              |Send device deleted|                     
 |                  |              |QMP event          |                     
 +------------------+              |                   |                     
                                   +-------------------+