ia64/linux-2.6.18-xen.hg

view Documentation/mtrr.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 MTRR (Memory Type Range Register) control
2 3 Jun 1999
3 Richard Gooch
4 <rgooch@atnf.csiro.au>
6 On Intel P6 family processors (Pentium Pro, Pentium II and later)
7 the Memory Type Range Registers (MTRRs) may be used to control
8 processor access to memory ranges. This is most useful when you have
9 a video (VGA) card on a PCI or AGP bus. Enabling write-combining
10 allows bus write transfers to be combined into a larger transfer
11 before bursting over the PCI/AGP bus. This can increase performance
12 of image write operations 2.5 times or more.
14 The Cyrix 6x86, 6x86MX and M II processors have Address Range
15 Registers (ARRs) which provide a similar functionality to MTRRs. For
16 these, the ARRs are used to emulate the MTRRs.
18 The AMD K6-2 (stepping 8 and above) and K6-3 processors have two
19 MTRRs. These are supported. The AMD Athlon family provide 8 Intel
20 style MTRRs.
22 The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. These
23 are supported.
25 The VIA Cyrix III and VIA C3 CPUs offer 8 Intel style MTRRs.
27 The CONFIG_MTRR option creates a /proc/mtrr file which may be used
28 to manipulate your MTRRs. Typically the X server should use
29 this. This should have a reasonably generic interface so that
30 similar control registers on other processors can be easily
31 supported.
34 There are two interfaces to /proc/mtrr: one is an ASCII interface
35 which allows you to read and write. The other is an ioctl()
36 interface. The ASCII interface is meant for administration. The
37 ioctl() interface is meant for C programs (i.e. the X server). The
38 interfaces are described below, with sample commands and C code.
40 ===============================================================================
41 Reading MTRRs from the shell:
43 % cat /proc/mtrr
44 reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1
45 reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1
46 ===============================================================================
47 Creating MTRRs from the C-shell:
48 # echo "base=0xf8000000 size=0x400000 type=write-combining" >! /proc/mtrr
49 or if you use bash:
50 # echo "base=0xf8000000 size=0x400000 type=write-combining" >| /proc/mtrr
52 And the result thereof:
53 % cat /proc/mtrr
54 reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1
55 reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1
56 reg02: base=0xf8000000 (3968MB), size= 4MB: write-combining, count=1
58 This is for video RAM at base address 0xf8000000 and size 4 megabytes. To
59 find out your base address, you need to look at the output of your X
60 server, which tells you where the linear framebuffer address is. A
61 typical line that you may get is:
63 (--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000000
65 Note that you should only use the value from the X server, as it may
66 move the framebuffer base address, so the only value you can trust is
67 that reported by the X server.
69 To find out the size of your framebuffer (what, you don't actually
70 know?), the following line will tell you:
72 (--) S3: videoram: 4096k
74 That's 4 megabytes, which is 0x400000 bytes (in hexadecimal).
75 A patch is being written for XFree86 which will make this automatic:
76 in other words the X server will manipulate /proc/mtrr using the
77 ioctl() interface, so users won't have to do anything. If you use a
78 commercial X server, lobby your vendor to add support for MTRRs.
79 ===============================================================================
80 Creating overlapping MTRRs:
82 %echo "base=0xfb000000 size=0x1000000 type=write-combining" >/proc/mtrr
83 %echo "base=0xfb000000 size=0x1000 type=uncachable" >/proc/mtrr
85 And the results: cat /proc/mtrr
86 reg00: base=0x00000000 ( 0MB), size= 64MB: write-back, count=1
87 reg01: base=0xfb000000 (4016MB), size= 16MB: write-combining, count=1
88 reg02: base=0xfb000000 (4016MB), size= 4kB: uncachable, count=1
90 Some cards (especially Voodoo Graphics boards) need this 4 kB area
91 excluded from the beginning of the region because it is used for
92 registers.
94 NOTE: You can only create type=uncachable region, if the first
95 region that you created is type=write-combining.
96 ===============================================================================
97 Removing MTRRs from the C-shell:
98 % echo "disable=2" >! /proc/mtrr
99 or using bash:
100 % echo "disable=2" >| /proc/mtrr
101 ===============================================================================
102 Reading MTRRs from a C program using ioctl()'s:
104 /* mtrr-show.c
106 Source file for mtrr-show (example program to show MTRRs using ioctl()'s)
108 Copyright (C) 1997-1998 Richard Gooch
110 This program is free software; you can redistribute it and/or modify
111 it under the terms of the GNU General Public License as published by
112 the Free Software Foundation; either version 2 of the License, or
113 (at your option) any later version.
115 This program is distributed in the hope that it will be useful,
116 but WITHOUT ANY WARRANTY; without even the implied warranty of
117 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
118 GNU General Public License for more details.
120 You should have received a copy of the GNU General Public License
121 along with this program; if not, write to the Free Software
122 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
124 Richard Gooch may be reached by email at rgooch@atnf.csiro.au
125 The postal address is:
126 Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia.
127 */
129 /*
130 This program will use an ioctl() on /proc/mtrr to show the current MTRR
131 settings. This is an alternative to reading /proc/mtrr.
134 Written by Richard Gooch 17-DEC-1997
136 Last updated by Richard Gooch 2-MAY-1998
139 */
140 #include <stdio.h>
141 #include <stdlib.h>
142 #include <string.h>
143 #include <sys/types.h>
144 #include <sys/stat.h>
145 #include <fcntl.h>
146 #include <sys/ioctl.h>
147 #include <errno.h>
148 #include <asm/mtrr.h>
150 #define TRUE 1
151 #define FALSE 0
152 #define ERRSTRING strerror (errno)
154 static char *mtrr_strings[MTRR_NUM_TYPES] =
155 {
156 "uncachable", /* 0 */
157 "write-combining", /* 1 */
158 "?", /* 2 */
159 "?", /* 3 */
160 "write-through", /* 4 */
161 "write-protect", /* 5 */
162 "write-back", /* 6 */
163 };
165 int main ()
166 {
167 int fd;
168 struct mtrr_gentry gentry;
170 if ( ( fd = open ("/proc/mtrr", O_RDONLY, 0) ) == -1 )
171 {
172 if (errno == ENOENT)
173 {
174 fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n",
175 stderr);
176 exit (1);
177 }
178 fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING);
179 exit (2);
180 }
181 for (gentry.regnum = 0; ioctl (fd, MTRRIOC_GET_ENTRY, &gentry) == 0;
182 ++gentry.regnum)
183 {
184 if (gentry.size < 1)
185 {
186 fprintf (stderr, "Register: %u disabled\n", gentry.regnum);
187 continue;
188 }
189 fprintf (stderr, "Register: %u base: 0x%lx size: 0x%lx type: %s\n",
190 gentry.regnum, gentry.base, gentry.size,
191 mtrr_strings[gentry.type]);
192 }
193 if (errno == EINVAL) exit (0);
194 fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING);
195 exit (3);
196 } /* End Function main */
197 ===============================================================================
198 Creating MTRRs from a C programme using ioctl()'s:
200 /* mtrr-add.c
202 Source file for mtrr-add (example programme to add an MTRRs using ioctl())
204 Copyright (C) 1997-1998 Richard Gooch
206 This program is free software; you can redistribute it and/or modify
207 it under the terms of the GNU General Public License as published by
208 the Free Software Foundation; either version 2 of the License, or
209 (at your option) any later version.
211 This program is distributed in the hope that it will be useful,
212 but WITHOUT ANY WARRANTY; without even the implied warranty of
213 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
214 GNU General Public License for more details.
216 You should have received a copy of the GNU General Public License
217 along with this program; if not, write to the Free Software
218 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
220 Richard Gooch may be reached by email at rgooch@atnf.csiro.au
221 The postal address is:
222 Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia.
223 */
225 /*
226 This programme will use an ioctl() on /proc/mtrr to add an entry. The first
227 available mtrr is used. This is an alternative to writing /proc/mtrr.
230 Written by Richard Gooch 17-DEC-1997
232 Last updated by Richard Gooch 2-MAY-1998
235 */
236 #include <stdio.h>
237 #include <string.h>
238 #include <stdlib.h>
239 #include <unistd.h>
240 #include <sys/types.h>
241 #include <sys/stat.h>
242 #include <fcntl.h>
243 #include <sys/ioctl.h>
244 #include <errno.h>
245 #include <asm/mtrr.h>
247 #define TRUE 1
248 #define FALSE 0
249 #define ERRSTRING strerror (errno)
251 static char *mtrr_strings[MTRR_NUM_TYPES] =
252 {
253 "uncachable", /* 0 */
254 "write-combining", /* 1 */
255 "?", /* 2 */
256 "?", /* 3 */
257 "write-through", /* 4 */
258 "write-protect", /* 5 */
259 "write-back", /* 6 */
260 };
262 int main (int argc, char **argv)
263 {
264 int fd;
265 struct mtrr_sentry sentry;
267 if (argc != 4)
268 {
269 fprintf (stderr, "Usage:\tmtrr-add base size type\n");
270 exit (1);
271 }
272 sentry.base = strtoul (argv[1], NULL, 0);
273 sentry.size = strtoul (argv[2], NULL, 0);
274 for (sentry.type = 0; sentry.type < MTRR_NUM_TYPES; ++sentry.type)
275 {
276 if (strcmp (argv[3], mtrr_strings[sentry.type]) == 0) break;
277 }
278 if (sentry.type >= MTRR_NUM_TYPES)
279 {
280 fprintf (stderr, "Illegal type: \"%s\"\n", argv[3]);
281 exit (2);
282 }
283 if ( ( fd = open ("/proc/mtrr", O_WRONLY, 0) ) == -1 )
284 {
285 if (errno == ENOENT)
286 {
287 fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n",
288 stderr);
289 exit (3);
290 }
291 fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING);
292 exit (4);
293 }
294 if (ioctl (fd, MTRRIOC_ADD_ENTRY, &sentry) == -1)
295 {
296 fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING);
297 exit (5);
298 }
299 fprintf (stderr, "Sleeping for 5 seconds so you can see the new entry\n");
300 sleep (5);
301 close (fd);
302 fputs ("I've just closed /proc/mtrr so now the new entry should be gone\n",
303 stderr);
304 } /* End Function main */
305 ===============================================================================