view Documentation/parport.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 The `parport' code provides parallel-port support under Linux. This
2 includes the ability to share one port between multiple device
3 drivers.
5 You can pass parameters to the parport code to override its automatic
6 detection of your hardware. This is particularly useful if you want
7 to use IRQs, since in general these can't be autoprobed successfully.
8 By default IRQs are not used even if they _can_ be probed. This is
9 because there are a lot of people using the same IRQ for their
10 parallel port and a sound card or network card.
12 The parport code is split into two parts: generic (which deals with
13 port-sharing) and architecture-dependent (which deals with actually
14 using the port).
17 Parport as modules
18 ==================
20 If you load the parport code as a module, say
22 # insmod parport
24 to load the generic parport code. You then must load the
25 architecture-dependent code with (for example):
27 # insmod parport_pc io=0x3bc,0x378,0x278 irq=none,7,auto
29 to tell the parport code that you want three PC-style ports, one at
30 0x3bc with no IRQ, one at 0x378 using IRQ 7, and one at 0x278 with an
31 auto-detected IRQ. Currently, PC-style (parport_pc), Sun `bpp',
32 Amiga, Atari, and MFC3 hardware is supported.
34 PCI parallel I/O card support comes from parport_pc. Base I/O
35 addresses should not be specified for supported PCI cards since they
36 are automatically detected.
39 KMod
40 ----
42 If you use kmod, you will find it useful to edit /etc/modprobe.conf.
43 Here is an example of the lines that need to be added:
45 alias parport_lowlevel parport_pc
46 options parport_pc io=0x378,0x278 irq=7,auto
48 KMod will then automatically load parport_pc (with the options
49 "io=0x378,0x278 irq=7,auto") whenever a parallel port device driver
50 (such as lp) is loaded.
52 Note that these are example lines only! You shouldn't in general need
53 to specify any options to parport_pc in order to be able to use a
54 parallel port.
57 Parport probe [optional]
58 -------------
60 In 2.2 kernels there was a module called parport_probe, which was used
61 for collecting IEEE 1284 device ID information. This has now been
62 enhanced and now lives with the IEEE 1284 support. When a parallel
63 port is detected, the devices that are connected to it are analysed,
64 and information is logged like this:
66 parport0: Printer, BJC-210 (Canon)
68 The probe information is available from files in /proc/sys/dev/parport/.
71 Parport linked into the kernel statically
72 =========================================
74 If you compile the parport code into the kernel, then you can use
75 kernel boot parameters to get the same effect. Add something like the
76 following to your LILO command line:
78 parport=0x3bc parport=0x378,7 parport=0x278,auto,nofifo
80 You can have many `parport=...' statements, one for each port you want
81 to add. Adding `parport=0' to the kernel command-line will disable
82 parport support entirely. Adding `parport=auto' to the kernel
83 command-line will make parport use any IRQ lines or DMA channels that
84 it auto-detects.
87 Files in /proc
88 ==============
90 If you have configured the /proc filesystem into your kernel, you will
91 see a new directory entry: /proc/sys/dev/parport. In there will be a
92 directory entry for each parallel port for which parport is
93 configured. In each of those directories are a collection of files
94 describing that parallel port.
96 The /proc/sys/dev/parport directory tree looks like:
98 parport
99 |-- default
100 | |-- spintime
101 | `-- timeslice
102 |-- parport0
103 | |-- autoprobe
104 | |-- autoprobe0
105 | |-- autoprobe1
106 | |-- autoprobe2
107 | |-- autoprobe3
108 | |-- devices
109 | | |-- active
110 | | `-- lp
111 | | `-- timeslice
112 | |-- base-addr
113 | |-- irq
114 | |-- dma
115 | |-- modes
116 | `-- spintime
117 `-- parport1
118 |-- autoprobe
119 |-- autoprobe0
120 |-- autoprobe1
121 |-- autoprobe2
122 |-- autoprobe3
123 |-- devices
124 | |-- active
125 | `-- ppa
126 | `-- timeslice
127 |-- base-addr
128 |-- irq
129 |-- dma
130 |-- modes
131 `-- spintime
134 File: Contents:
136 devices/active A list of the device drivers using that port. A "+"
137 will appear by the name of the device currently using
138 the port (it might not appear against any). The
139 string "none" means that there are no device drivers
140 using that port.
142 base-addr Parallel port's base address, or addresses if the port
143 has more than one in which case they are separated
144 with tabs. These values might not have any sensible
145 meaning for some ports.
147 irq Parallel port's IRQ, or -1 if none is being used.
149 dma Parallel port's DMA channel, or -1 if none is being
150 used.
152 modes Parallel port's hardware modes, comma-separated,
153 meaning:
155 PCSPP PC-style SPP registers are available.
156 TRISTATE Port is bidirectional.
157 COMPAT Hardware acceleration for printers is
158 available and will be used.
159 EPP Hardware acceleration for EPP protocol
160 is available and will be used.
161 ECP Hardware acceleration for ECP protocol
162 is available and will be used.
163 DMA DMA is available and will be used.
165 Note that the current implementation will only take
166 advantage of COMPAT and ECP modes if it has an IRQ
167 line to use.
169 autoprobe Any IEEE-1284 device ID information that has been
170 acquired from the (non-IEEE 1284.3) device.
172 autoprobe[0-3] IEEE 1284 device ID information retrieved from
173 daisy-chain devices that conform to IEEE 1284.3.
175 spintime The number of microseconds to busy-loop while waiting
176 for the peripheral to respond. You might find that
177 adjusting this improves performance, depending on your
178 peripherals. This is a port-wide setting, i.e. it
179 applies to all devices on a particular port.
181 timeslice The number of milliseconds that a device driver is
182 allowed to keep a port claimed for. This is advisory,
183 and driver can ignore it if it must.
185 default/* The defaults for spintime and timeslice. When a new
186 port is registered, it picks up the default spintime.
187 When a new device is registered, it picks up the
188 default timeslice.
190 Device drivers
191 ==============
193 Once the parport code is initialised, you can attach device drivers to
194 specific ports. Normally this happens automatically; if the lp driver
195 is loaded it will create one lp device for each port found. You can
196 override this, though, by using parameters either when you load the lp
197 driver:
199 # insmod lp parport=0,2
201 or on the LILO command line:
203 lp=parport0 lp=parport2
205 Both the above examples would inform lp that you want /dev/lp0 to be
206 the first parallel port, and /dev/lp1 to be the _third_ parallel port,
207 with no lp device associated with the second port (parport1). Note
208 that this is different to the way older kernels worked; there used to
209 be a static association between the I/O port address and the device
210 name, so /dev/lp0 was always the port at 0x3bc. This is no longer the
211 case - if you only have one port, it will default to being /dev/lp0,
212 regardless of base address.
214 Also:
216 * If you selected the IEEE 1284 support at compile time, you can say
217 `lp=auto' on the kernel command line, and lp will create devices
218 only for those ports that seem to have printers attached.
220 * If you give PLIP the `timid' parameter, either with `plip=timid' on
221 the command line, or with `insmod plip timid=1' when using modules,
222 it will avoid any ports that seem to be in use by other devices.
224 * IRQ autoprobing works only for a few port types at the moment.
226 Reporting printer problems with parport
227 =======================================
229 If you are having problems printing, please go through these steps to
230 try to narrow down where the problem area is.
232 When reporting problems with parport, really you need to give all of
233 the messages that parport_pc spits out when it initialises. There are
234 several code paths:
236 o polling
237 o interrupt-driven, protocol in software
238 o interrupt-driven, protocol in hardware using PIO
239 o interrupt-driven, protocol in hardware using DMA
241 The kernel messages that parport_pc logs give an indication of which
242 code path is being used. (They could be a lot better actually..)
244 For normal printer protocol, having IEEE 1284 modes enabled or not
245 should not make a difference.
247 To turn off the 'protocol in hardware' code paths, disable
248 CONFIG_PARPORT_PC_FIFO. Note that when they are enabled they are not
249 necessarily _used_; it depends on whether the hardware is available,
250 enabled by the BIOS, and detected by the driver.
252 So, to start with, disable CONFIG_PARPORT_PC_FIFO, and load parport_pc
253 with 'irq=none'. See if printing works then. It really should,
254 because this is the simplest code path.
256 If that works fine, try with 'io=0x378 irq=7' (adjust for your
257 hardware), to make it use interrupt-driven in-software protocol.
259 If _that_ works fine, then one of the hardware modes isn't working
260 right. Enable CONFIG_PARPORT_PC_FIFO (no, it isn't a module option,
261 and yes, it should be), set the port to ECP mode in the BIOS and note
262 the DMA channel, and try with:
264 io=0x378 irq=7 dma=none (for PIO)
265 io=0x378 irq=7 dma=3 (for DMA)
266 --
267 philb@gnu.org
268 tim@cyberelk.net