view Documentation/floppy.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 This file describes the floppy driver.
3 FAQ list:
4 =========
6 A FAQ list may be found in the fdutils package (see below), and also
7 at <http://fdutils.linux.lu/faq.html>.
10 LILO configuration options (Thinkpad users, read this)
11 ======================================================
13 The floppy driver is configured using the 'floppy=' option in
14 lilo. This option can be typed at the boot prompt, or entered in the
15 lilo configuration file.
17 Example: If your kernel is called linux-2.6.9, type the following line
18 at the lilo boot prompt (if you have a thinkpad):
20 linux-2.6.9 floppy=thinkpad
22 You may also enter the following line in /etc/lilo.conf, in the description
23 of linux-2.6.9:
25 append = "floppy=thinkpad"
27 Several floppy related options may be given, example:
29 linux-2.6.9 floppy=daring floppy=two_fdc
30 append = "floppy=daring floppy=two_fdc"
32 If you give options both in the lilo config file and on the boot
33 prompt, the option strings of both places are concatenated, the boot
34 prompt options coming last. That's why there are also options to
35 restore the default behavior.
38 Module configuration options
39 ============================
41 If you use the floppy driver as a module, use the following syntax:
42 modprobe floppy <options>
44 Example:
45 modprobe floppy omnibook messages
47 If you need certain options enabled every time you load the floppy driver,
48 you can put:
50 options floppy omnibook messages
52 in /etc/modprobe.conf.
55 The floppy driver related options are:
57 floppy=asus_pci
58 Sets the bit mask to allow only units 0 and 1. (default)
60 floppy=daring
61 Tells the floppy driver that you have a well behaved floppy controller.
62 This allows more efficient and smoother operation, but may fail on
63 certain controllers. This may speed up certain operations.
65 floppy=0,daring
66 Tells the floppy driver that your floppy controller should be used
67 with caution.
69 floppy=one_fdc
70 Tells the floppy driver that you have only one floppy controller.
71 (default)
73 floppy=two_fdc
74 floppy=<address>,two_fdc
75 Tells the floppy driver that you have two floppy controllers.
76 The second floppy controller is assumed to be at <address>.
77 This option is not needed if the second controller is at address
78 0x370, and if you use the 'cmos' option.
80 floppy=thinkpad
81 Tells the floppy driver that you have a Thinkpad. Thinkpads use an
82 inverted convention for the disk change line.
84 floppy=0,thinkpad
85 Tells the floppy driver that you don't have a Thinkpad.
87 floppy=omnibook
88 floppy=nodma
89 Tells the floppy driver not to use Dma for data transfers.
90 This is needed on HP Omnibooks, which don't have a workable
91 DMA channel for the floppy driver. This option is also useful
92 if you frequently get "Unable to allocate DMA memory" messages.
93 Indeed, dma memory needs to be continuous in physical memory,
94 and is thus harder to find, whereas non-dma buffers may be
95 allocated in virtual memory. However, I advise against this if
96 you have an FDC without a FIFO (8272A or 82072). 82072A and
97 later are OK. You also need at least a 486 to use nodma.
98 If you use nodma mode, I suggest you also set the FIFO
99 threshold to 10 or lower, in order to limit the number of data
100 transfer interrupts.
102 If you have a FIFO-able FDC, the floppy driver automatically
103 falls back on non DMA mode if no DMA-able memory can be found.
104 If you want to avoid this, explicitly ask for 'yesdma'.
106 floppy=yesdma
107 Tells the floppy driver that a workable DMA channel is available.
108 (default)
110 floppy=nofifo
111 Disables the FIFO entirely. This is needed if you get "Bus
112 master arbitration error" messages from your Ethernet card (or
113 from other devices) while accessing the floppy.
115 floppy=usefifo
116 Enables the FIFO. (default)
118 floppy=<threshold>,fifo_depth
119 Sets the FIFO threshold. This is mostly relevant in DMA
120 mode. If this is higher, the floppy driver tolerates more
121 interrupt latency, but it triggers more interrupts (i.e. it
122 imposes more load on the rest of the system). If this is
123 lower, the interrupt latency should be lower too (faster
124 processor). The benefit of a lower threshold is less
125 interrupts.
127 To tune the fifo threshold, switch on over/underrun messages
128 using 'floppycontrol --messages'. Then access a floppy
129 disk. If you get a huge amount of "Over/Underrun - retrying"
130 messages, then the fifo threshold is too low. Try with a
131 higher value, until you only get an occasional Over/Underrun.
132 It is a good idea to compile the floppy driver as a module
133 when doing this tuning. Indeed, it allows to try different
134 fifo values without rebooting the machine for each test. Note
135 that you need to do 'floppycontrol --messages' every time you
136 re-insert the module.
138 Usually, tuning the fifo threshold should not be needed, as
139 the default (0xa) is reasonable.
141 floppy=<drive>,<type>,cmos
142 Sets the CMOS type of <drive> to <type>. This is mandatory if
143 you have more than two floppy drives (only two can be
144 described in the physical CMOS), or if your BIOS uses
145 non-standard CMOS types. The CMOS types are:
147 0 - Use the value of the physical CMOS
148 1 - 5 1/4 DD
149 2 - 5 1/4 HD
150 3 - 3 1/2 DD
151 4 - 3 1/2 HD
152 5 - 3 1/2 ED
153 6 - 3 1/2 ED
154 16 - unknown or not installed
156 (Note: there are two valid types for ED drives. This is because 5 was
157 initially chosen to represent floppy *tapes*, and 6 for ED drives.
158 AMI ignored this, and used 5 for ED drives. That's why the floppy
159 driver handles both.)
161 floppy=unexpected_interrupts
162 Print a warning message when an unexpected interrupt is received.
163 (default)
165 floppy=no_unexpected_interrupts
166 floppy=L40SX
167 Don't print a message when an unexpected interrupt is received. This
168 is needed on IBM L40SX laptops in certain video modes. (There seems
169 to be an interaction between video and floppy. The unexpected
170 interrupts affect only performance, and can be safely ignored.)
172 floppy=broken_dcl
173 Don't use the disk change line, but assume that the disk was
174 changed whenever the device node is reopened. Needed on some
175 boxes where the disk change line is broken or unsupported.
176 This should be regarded as a stopgap measure, indeed it makes
177 floppy operation less efficient due to unneeded cache
178 flushings, and slightly more unreliable. Please verify your
179 cable, connection and jumper settings if you have any DCL
180 problems. However, some older drives, and also some laptops
181 are known not to have a DCL.
183 floppy=debug
184 Print debugging messages.
186 floppy=messages
187 Print informational messages for some operations (disk change
188 notifications, warnings about over and underruns, and about
189 autodetection).
191 floppy=silent_dcl_clear
192 Uses a less noisy way to clear the disk change line (which
193 doesn't involve seeks). Implied by 'daring' option.
195 floppy=<nr>,irq
196 Sets the floppy IRQ to <nr> instead of 6.
198 floppy=<nr>,dma
199 Sets the floppy DMA channel to <nr> instead of 2.
201 floppy=slow
202 Use PS/2 stepping rate:
203 " PS/2 floppies have much slower step rates than regular floppies.
204 It's been recommended that take about 1/4 of the default speed
205 in some more extreme cases."
208 Supporting utilities and additional documentation:
209 ==================================================
211 Additional parameters of the floppy driver can be configured at
212 runtime. Utilities which do this can be found in the fdutils package.
213 This package also contains a new version of mtools which allows to
214 access high capacity disks (up to 1992K on a high density 3 1/2 disk!).
215 It also contains additional documentation about the floppy driver.
217 The latest version can be found at fdutils homepage:
218 http://fdutils.linux.lu
220 The fdutils releases can be found at:
221 http://fdutils.linux.lu/download.html
222 http://www.tux.org/pub/knaff/fdutils/
223 ftp://metalab.unc.edu/pub/Linux/utils/disk-management/
225 Reporting problems about the floppy driver
226 ==========================================
228 If you have a question or a bug report about the floppy driver, mail
229 me at Alain.Knaff@poboxes.com . If you post to Usenet, preferably use
230 comp.os.linux.hardware. As the volume in these groups is rather high,
231 be sure to include the word "floppy" (or "FLOPPY") in the subject
232 line. If the reported problem happens when mounting floppy disks, be
233 sure to mention also the type of the filesystem in the subject line.
235 Be sure to read the FAQ before mailing/posting any bug reports!
237 Alain
239 Changelog
240 =========
242 10-30-2004 : Cleanup, updating, add reference to module configuration.
243 James Nelson <james4765@gmail.com>
245 6-3-2000 : Original Document