ia64/linux-2.6.18-xen.hg

view Documentation/hayes-esp.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
1 HAYES ESP DRIVER VERSION 2.1
3 A big thanks to the people at Hayes, especially Alan Adamson. Their support
4 has enabled me to provide enhancements to the driver.
6 Please report your experiences with this driver to me (arobinso@nyx.net). I
7 am looking for both positive and negative feedback.
9 *** IMPORTANT CHANGES FOR 2.1 ***
10 Support for PIO mode. Five situations will cause PIO mode to be used:
11 1) A multiport card is detected. PIO mode will always be used. (8 port cards
12 do not support DMA).
13 2) The DMA channel is set to an invalid value (anything other than 1 or 3).
14 3) The DMA buffer/channel could not be allocated. The port will revert to PIO
15 mode until it is reopened.
16 4) Less than a specified number of bytes need to be transferred to/from the
17 FIFOs. PIO mode will be used for that transfer only.
18 5) A port needs to do a DMA transfer and another port is already using the
19 DMA channel. PIO mode will be used for that transfer only.
21 Since the Hayes ESP seems to conflict with other cards (notably sound cards)
22 when using DMA, DMA is turned off by default. To use DMA, it must be turned
23 on explicitly, either with the "dma=" option described below or with
24 setserial. A multiport card can be forced into DMA mode by using setserial;
25 however, most multiport cards don't support DMA.
27 The latest version of setserial allows the enhanced configuration of the ESP
28 card to be viewed and modified.
29 ***
31 This package contains the files needed to compile a module to support the Hayes
32 ESP card. The drivers are basically a modified version of the serial drivers.
34 Features:
36 - Uses the enhanced mode of the ESP card, allowing a wider range of
37 interrupts and features than compatibility mode
38 - Uses DMA and 16 bit PIO mode to transfer data to and from the ESP's FIFOs,
39 reducing CPU load
40 - Supports primary and secondary ports
43 If the driver is compiled as a module, the IRQs to use can be specified by
44 using the irq= option. The format is:
46 irq=[0x100],[0x140],[0x180],[0x200],[0x240],[0x280],[0x300],[0x380]
48 The address in brackets is the base address of the card. The IRQ of
49 nonexistent cards can be set to 0. If an IRQ of a card that does exist is set
50 to 0, the driver will attempt to guess at the correct IRQ. For example, to set
51 the IRQ of the card at address 0x300 to 12, the insmod command would be:
53 insmod esp irq=0,0,0,0,0,0,12,0
55 The custom divisor can be set by using the divisor= option. The format is the
56 same as for the irq= option. Each divisor value is a series of hex digits,
57 with each digit representing the divisor to use for a corresponding port. The
58 divisor value is constructed RIGHT TO LEFT. Specifying a nonzero divisor value
59 will automatically set the spd_cust flag. To calculate the divisor to use for
60 a certain baud rate, divide the port's base baud (generally 921600) by the
61 desired rate. For example, to set the divisor of the primary port at 0x300 to
62 4 and the divisor of the secondary port at 0x308 to 8, the insmod command would
63 be:
65 insmod esp divisor=0,0,0,0,0,0,0x84,0
67 The dma= option can be used to set the DMA channel. The channel can be either
68 1 or 3. Specifying any other value will force the driver to use PIO mode.
69 For example, to set the DMA channel to 3, the insmod command would be:
71 insmod esp dma=3
73 The rx_trigger= and tx_trigger= options can be used to set the FIFO trigger
74 levels. They specify when the ESP card should send an interrupt. Larger
75 values will decrease the number of interrupts; however, a value too high may
76 result in data loss. Valid values are 1 through 1023, with 768 being the
77 default. For example, to set the receive trigger level to 512 bytes and the
78 transmit trigger level to 700 bytes, the insmod command would be:
80 insmod esp rx_trigger=512 tx_trigger=700
82 The flow_off= and flow_on= options can be used to set the hardware flow off/
83 flow on levels. The flow on level must be lower than the flow off level, and
84 the flow off level should be higher than rx_trigger. Valid values are 1
85 through 1023, with 1016 being the default flow off level and 944 being the
86 default flow on level. For example, to set the flow off level to 1000 bytes
87 and the flow on level to 935 bytes, the insmod command would be:
89 insmod esp flow_off=1000 flow_on=935
91 The rx_timeout= option can be used to set the receive timeout value. This
92 value indicates how long after receiving the last character that the ESP card
93 should wait before signalling an interrupt. Valid values are 0 though 255,
94 with 128 being the default. A value too high will increase latency, and a
95 value too low will cause unnecessary interrupts. For example, to set the
96 receive timeout to 255, the insmod command would be:
98 insmod esp rx_timeout=255
100 The pio_threshold= option sets the threshold (in number of characters) for
101 using PIO mode instead of DMA mode. For example, if this value is 32,
102 transfers of 32 bytes or less will always use PIO mode.
104 insmod esp pio_threshold=32
106 Multiple options can be listed on the insmod command line by separating each
107 option with a space. For example:
109 insmod esp dma=3 trigger=512
111 The esp module can be automatically loaded when needed. To cause this to
112 happen, add the following lines to /etc/modprobe.conf (replacing the last line
113 with options for your configuration):
115 alias char-major-57 esp
116 alias char-major-58 esp
117 options esp irq=0,0,0,0,0,0,3,0 divisor=0,0,0,0,0,0,0x4,0
119 You may also need to run 'depmod -a'.
121 Devices must be created manually. To create the devices, note the output from
122 the module after it is inserted. The output will appear in the location where
123 kernel messages usually appear (usually /var/adm/messages). Create two devices
124 for each 'tty' mentioned, one with major of 57 and the other with major of 58.
125 The minor number should be the same as the tty number reported. The commands
126 would be (replace ? with the tty number):
128 mknod /dev/ttyP? c 57 ?
129 mknod /dev/cup? c 58 ?
131 For example, if the following line appears:
133 Oct 24 18:17:23 techno kernel: ttyP8 at 0x0140 (irq = 3) is an ESP primary port
135 ...two devices should be created:
137 mknod /dev/ttyP8 c 57 8
138 mknod /dev/cup8 c 58 8
140 You may need to set the permissions on the devices:
142 chmod 666 /dev/ttyP*
143 chmod 666 /dev/cup*
145 The ESP module and the serial module should not conflict (they can be used at
146 the same time). After the ESP module has been loaded the ports on the ESP card
147 will no longer be accessible by the serial driver.
149 If I/O errors are experienced when accessing the port, check for IRQ and DMA
150 conflicts ('cat /proc/interrupts' and 'cat /proc/dma' for a list of IRQs and
151 DMAs currently in use).
153 Enjoy!
154 Andrew J. Robinson <arobinso@nyx.net>