view Documentation/dell_rbu.txt @ 897:329ea0ccb344

balloon: try harder to balloon up under memory pressure.

Currently if the balloon driver is unable to increase the guest's
reservation it assumes the failure was due to reaching its full
allocation, gives up on the ballooning operation and records the limit
it reached as the "hard limit". The driver will not try again until
the target is set again (even to the same value).

However it is possible that ballooning has in fact failed due to
memory pressure in the host and therefore it is desirable to keep
attempting to reach the target in case memory becomes available. The
most likely scenario is that some guests are ballooning down while
others are ballooning up and therefore there is temporary memory
pressure while things stabilise. You would not expect a well behaved
toolstack to ask a domain to balloon to more than its allocation nor
would you expect it to deliberately over-commit memory by setting
balloon targets which exceed the total host memory.

This patch drops the concept of a hard limit and causes the balloon
driver to retry increasing the reservation on a timer in the same
manner as when decreasing the reservation.

Also if we partially succeed in increasing the reservation
(i.e. receive less pages than we asked for) then we may as well keep
those pages rather than returning them to Xen.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Fri Jun 05 14:01:20 2009 +0100 (2009-06-05)
parents 831230e53067
line source
1 Purpose:
2 Demonstrate the usage of the new open sourced rbu (Remote BIOS Update) driver
3 for updating BIOS images on Dell servers and desktops.
5 Scope:
6 This document discusses the functionality of the rbu driver only.
7 It does not cover the support needed from aplications to enable the BIOS to
8 update itself with the image downloaded in to the memory.
10 Overview:
11 This driver works with Dell OpenManage or Dell Update Packages for updating
12 the BIOS on Dell servers (starting from servers sold since 1999), desktops
13 and notebooks (starting from those sold in 2005).
14 Please go to http://support.dell.com register and you can find info on
15 OpenManage and Dell Update packages (DUP).
16 Libsmbios can also be used to update BIOS on Dell systems go to
17 http://linux.dell.com/libsmbios/ for details.
19 Dell_RBU driver supports BIOS update using the monilothic image and packetized
20 image methods. In case of moniolithic the driver allocates a contiguous chunk
21 of physical pages having the BIOS image. In case of packetized the app
22 using the driver breaks the image in to packets of fixed sizes and the driver
23 would place each packet in contiguous physical memory. The driver also
24 maintains a link list of packets for reading them back.
25 If the dell_rbu driver is unloaded all the allocated memory is freed.
27 The rbu driver needs to have an application (as mentioned above)which will
28 inform the BIOS to enable the update in the next system reboot.
30 The user should not unload the rbu driver after downloading the BIOS image
31 or updating.
33 The driver load creates the following directories under the /sys file system.
34 /sys/class/firmware/dell_rbu/loading
35 /sys/class/firmware/dell_rbu/data
36 /sys/devices/platform/dell_rbu/image_type
37 /sys/devices/platform/dell_rbu/data
38 /sys/devices/platform/dell_rbu/packet_size
40 The driver supports two types of update mechanism; monolithic and packetized.
41 These update mechanism depends upon the BIOS currently running on the system.
42 Most of the Dell systems support a monolithic update where the BIOS image is
43 copied to a single contiguous block of physical memory.
44 In case of packet mechanism the single memory can be broken in smaller chuks
45 of contiguous memory and the BIOS image is scattered in these packets.
47 By default the driver uses monolithic memory for the update type. This can be
48 changed to packets during the driver load time by specifying the load
49 parameter image_type=packet. This can also be changed later as below
50 echo packet > /sys/devices/platform/dell_rbu/image_type
52 In packet update mode the packet size has to be given before any packets can
53 be downloaded. It is done as below
54 echo XXXX > /sys/devices/platform/dell_rbu/packet_size
55 In the packet update mechanism, the user neesd to create a new file having
56 packets of data arranged back to back. It can be done as follows
57 The user creates packets header, gets the chunk of the BIOS image and
58 placs it next to the packetheader; now, the packetheader + BIOS image chunk
59 added to geather should match the specified packet_size. This makes one
60 packet, the user needs to create more such packets out of the entire BIOS
61 image file and then arrange all these packets back to back in to one single
62 file.
63 This file is then copied to /sys/class/firmware/dell_rbu/data.
64 Once this file gets to the driver, the driver extracts packet_size data from
65 the file and spreads it accross the physical memory in contiguous packet_sized
66 space.
67 This method makes sure that all the packets get to the driver in a single operation.
69 In monolithic update the user simply get the BIOS image (.hdr file) and copies
70 to the data file as is without any change to the BIOS image itself.
72 Do the steps below to download the BIOS image.
73 1) echo 1 > /sys/class/firmware/dell_rbu/loading
74 2) cp bios_image.hdr /sys/class/firmware/dell_rbu/data
75 3) echo 0 > /sys/class/firmware/dell_rbu/loading
77 The /sys/class/firmware/dell_rbu/ entries will remain till the following is
78 done.
79 echo -1 > /sys/class/firmware/dell_rbu/loading.
80 Until this step is completed the driver cannot be unloaded.
81 Also echoing either mono ,packet or init in to image_type will free up the
82 memory allocated by the driver.
84 If an user by accident executes steps 1 and 3 above without executing step 2;
85 it will make the /sys/class/firmware/dell_rbu/ entries to disappear.
86 The entries can be recreated by doing the following
87 echo init > /sys/devices/platform/dell_rbu/image_type
88 NOTE: echoing init in image_type does not change it original value.
90 Also the driver provides /sys/devices/platform/dell_rbu/data readonly file to
91 read back the image downloaded.
93 NOTE:
94 This driver requires a patch for firmware_class.c which has the modified
95 request_firmware_nowait function.
96 Also after updating the BIOS image an user mdoe application neeeds to execute
97 code which message the BIOS update request to the BIOS. So on the next reboot
98 the BIOS knows about the new image downloaded and it updates it self.
99 Also don't unload the rbu drive if the image has to be updated.