ia64/linux-2.6.18-xen.hg

view Documentation/tipar.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
children
line source
2 Parallel link cable for Texas Instruments handhelds
3 ===================================================
6 Author: Romain Lievin
7 Homepage: http://lpg.ticalc.org/prj_tidev/index.html
10 INTRODUCTION:
12 This is a driver for the very common home-made parallel link cable, a cable
13 designed for connecting TI8x/9x graphing calculators (handhelds) to a computer
14 or workstation (Alpha, Sparc). Given that driver is built on parport, the
15 parallel port abstraction layer, this driver is architecture-independent.
17 It can also be used with another device plugged on the same port (such as a
18 ZIP drive). I have a 100MB ZIP and both of them work fine!
20 If you need more information, please visit the 'TI drivers' homepage at the URL
21 above.
23 WHAT YOU NEED:
25 A TI calculator and a program capable of communicating with your calculator.
27 TiLP will work for sure (since I am its developer!). yal92 may be able to use
28 it by changing tidev for tipar (may require some hacking...).
30 HOW TO USE IT:
32 You must have first compiled parport support (CONFIG_PARPORT_DEV): either
33 compiled in your kernel, either as a module.
35 Next, (as root):
37 modprobe parport
38 modprobe tipar
40 If it is not already there (it usually is), create the device:
42 mknod /dev/tipar0 c 115 0
43 mknod /dev/tipar1 c 115 1
44 mknod /dev/tipar2 c 115 2
46 You will have to set permissions on this device to allow you to read/write
47 from it:
49 chmod 666 /dev/tipar[0..2]
51 Now you are ready to run a linking program such as TiLP. Be sure to configure
52 it properly (RTFM).
54 MODULE PARAMETERS:
56 You can set these with: modprobe tipar NAME=VALUE
57 There is currently no way to set these on a per-cable basis.
59 NAME: timeout
60 TYPE: integer
61 DEFAULT: 15
62 DESC: Timeout value in tenth of seconds. If no data is available once this
63 time has expired then the driver will return with a timeout error.
65 NAME: delay
66 TYPE: integer
67 DEFAULT: 10
68 DESC: Inter-bit delay in micro-seconds. A lower value gives an higher data
69 rate but makes transmission less reliable.
71 These parameters can be changed at run time by any program via ioctl(2) calls
72 as listed in ./include/linux/ticable.h.
74 Rather than write 50 pages describing the ioctl() and so on, it is
75 perhaps more useful you look at ticables library (dev_link.c) that demonstrates
76 how to use them, and demonstrates the features of the driver. This is
77 probably a lot more useful to people interested in writing applications
78 that will be using this driver.
80 QUIRKS/BUGS:
82 None.
84 HOW TO CONTACT US:
86 You can email me at roms@lpg.ticalc.org. Please prefix the subject line
87 with "TIPAR: " so that I am certain to notice your message.
88 You can also mail JB at jb@jblache.org. He packaged these drivers for Debian.
90 CREDITS:
92 The code is based on tidev.c & parport.c.
93 The driver has been developed independently of Texas Instruments.