1 AMD64 specific boot options
3 There are many others (usually documented in driver documentation), but
4 only the AMD64 specific ones are listed here.
8 mce=off disable machine check
9 mce=bootlog Enable logging of machine checks left over from booting.
10 Disabled by default on AMD because some BIOS leave bogus ones.
11 If your BIOS doesn't do that it's a good idea to enable though
12 to make sure you log even machine check events that result
13 in a reboot. On Intel systems it is enabled by default.
15 Disable boot machine check logging.
16 mce=tolerancelevel (number)
17 0: always panic on uncorrected errors, log corrected errors
18 1: panic or SIGBUS on uncorrected errors, log corrected errors
19 2: SIGBUS or log uncorrected errors, log corrected errors
20 3: never panic or SIGBUS, log all errors (for testing only)
22 Can be also set using sysfs which is preferable.
24 nomce (for compatibility with i386): same as mce=off
26 Everything else is in sysfs now.
30 apic Use IO-APIC. Default
32 noapic Don't use the IO-APIC.
34 disableapic Don't use the local APIC
36 nolapic Don't use the local APIC (alias for i386 compatibility)
38 pirq=... See Documentation/i386/IO-APIC.txt
40 noapictimer Don't set up the APIC timer
42 no_timer_check Don't check the IO-APIC timer. This can work around
43 problems with incorrect timer initialization on some boards.
45 apicmaintimer Run time keeping from the local APIC timer instead
46 of using the PIT/HPET interrupt for this. This is useful
47 when the PIT/HPET interrupts are unreliable.
49 noapicmaintimer Don't do time keeping using the APIC timer.
50 Useful when this option was auto selected, but doesn't work.
53 Do APIC timer calibration using the pmtimer. Implies
54 apicmaintimer. Useful when your PIT timer is totally
57 disable_8254_timer / enable_8254_timer
58 Enable interrupt 0 timer routing over the 8254 in addition to over
59 the IO-APIC. The kernel tries to set a sensible default.
63 syntax: earlyprintk=vga
64 earlyprintk=serial[,ttySn[,baudrate]]
66 The early console is useful when the kernel crashes before the
67 normal console is initialized. It is not enabled by
68 default because it has some cosmetic problems.
69 Append ,keep to not disable it when the real console takes over.
70 Only vga or serial at a time, not both.
71 Currently only ttyS0 and ttyS1 are supported.
72 Interaction with the standard serial driver is not very good.
73 The VGA output is eventually overwritten by the real console.
78 Don't use the CPU time stamp counter to read the wall time.
79 This can be used to work around timing problems on multiprocessor systems
80 with not properly synchronized CPUs.
83 Report when timer interrupts are lost because some code turned off
84 interrupts for too long.
86 nmi_watchdog=NUMBER[,panic]
88 0 don't use an NMI watchdog
89 1 use the IO-APIC timer for the NMI watchdog
90 2 use the local APIC for the NMI watchdog using a performance counter. Note
91 This will use one performance counter and the local APIC's performance
93 When panic is specified panic when an NMI watchdog timeout occurs.
94 This is useful when you use a panic=... timeout and need the box
98 Don't use the HPET timer.
103 Don't do power saving in the idle loop using HLT, but poll for rescheduling
104 event. This will make the CPUs eat a lot more power, but may be useful
105 to get slightly better performance in multiprocessor benchmarks. It also
106 makes some profiling using performance counters more accurate.
107 Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
108 CPUs) this option has no performance advantage over the normal idle loop.
109 It may also interact badly with hyperthreading.
113 reboot=b[ios] | t[riple] | k[bd] | a[cpi] [, [w]arm | [c]old]
114 bios Use the CPU reboot vector for warm reset
115 warm Don't set the cold reboot flag
116 cold Set the cold reboot flag
117 triple Force a triple fault (init)
118 kbd Use the keyboard controller. cold reset (default)
119 acpi Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
120 ACPI reset does not work, the reboot path attempts the reset using
121 the keyboard controller.
123 Using warm reset will be much faster especially on big memory
124 systems because the BIOS will not go through the memory check.
125 Disadvantage is that not all hardware will be completely reinitialized
126 on reboot so there may be boot problems on some systems.
130 Don't stop other CPUs on reboot. This can make reboot more reliable
133 Non Executable Mappings
142 additional_cpus=NUM Allow NUM more CPUs for hotplug
143 (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
147 numa=off Only set up a single NUMA node spanning all memory.
149 numa=noacpi Don't parse the SRAT table for NUMA setup
152 If a number, fakes CMDLINE nodes and ignores NUMA setup of the
153 actual machine. Otherwise, system memory is configured
154 depending on the sizes and coefficients listed. For example:
155 numa=fake=2*512,1024,4*256,*128
156 gives two 512M nodes, a 1024M node, four 256M nodes, and the
157 rest split into 128M chunks. If the last character of CMDLINE
158 is a *, the remaining memory is divided up equally among its
161 gives two 512M nodes and the rest split into two nodes.
162 Otherwise, the remaining system RAM is allocated to an
166 Only allow hotadd memory to preallocate page structures upto
167 percent of already available memory.
168 numa=hotadd=0 will disable hotadd memory.
172 acpi=off Don't enable ACPI
173 acpi=ht Use ACPI boot table parsing, but don't enable ACPI
175 acpi=force Force ACPI on (currently not needed)
177 acpi=strict Disable out of spec ACPI workarounds.
179 acpi_sci={edge,level,high,low} Set up ACPI SCI interrupt.
181 acpi=noirq Don't route interrupts
185 pci=off Don't use PCI
186 pci=conf1 Use conf1 access.
187 pci=conf2 Use conf2 access.
189 pci=assign-busses Assign busses
190 pci=irqmask=MASK Set PCI interrupt mask to MASK
191 pci=lastbus=NUMBER Scan upto NUMBER busses, no matter what the mptable says.
192 pci=noacpi Don't use ACPI to set up PCI interrupt routing.
194 IOMMU (input/output memory management unit)
196 Currently four x86-64 PCI-DMA mapping implementations exist:
198 1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
199 (e.g. because you have < 3 GB memory).
200 Kernel boot message: "PCI-DMA: Disabling IOMMU"
202 2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.
203 Kernel boot message: "PCI-DMA: using GART IOMMU"
205 3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
206 e.g. if there is no hardware IOMMU in the system and it is need because
207 you have >3GB memory or told the kernel to us it (iommu=soft))
208 Kernel boot message: "PCI-DMA: Using software bounce buffering
211 4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
212 pSeries and xSeries servers. This hardware IOMMU supports DMA address
213 mapping with memory protection, etc.
214 Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
216 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
217 [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
218 [,noaperture][,calgary]
220 General iommu options:
221 off Don't initialize and use any kind of IOMMU.
222 noforce Don't force hardware IOMMU usage when it is not needed.
224 force Force the use of the hardware IOMMU even when it is
225 not actually needed (e.g. because < 3 GB memory).
226 soft Use software bounce buffering (SWIOTLB) (default for
227 Intel machines). This can be used to prevent the usage
228 of an available hardware IOMMU.
230 iommu options only relevant to the AMD GART hardware IOMMU:
231 <size> Set the size of the remapping area in bytes.
232 allowed Overwrite iommu off workarounds for specific chipsets.
233 fullflush Flush IOMMU on each allocation (default).
234 nofullflush Don't use IOMMU fullflush.
235 leak Turn on simple iommu leak tracing (only when
236 CONFIG_IOMMU_LEAK is on). Default number of leak pages
238 memaper[=<order>] Allocate an own aperture over RAM with size 32MB<<order.
239 (default: order=1, i.e. 64MB)
240 merge Do scatter-gather (SG) merging. Implies "force"
242 nomerge Don't do scatter-gather (SG) merging.
243 noaperture Ask the IOMMU not to touch the aperture for AGP.
244 forcesac Force single-address cycle (SAC) mode for masks <40bits
246 noagp Don't initialize the AGP driver and use full aperture.
247 allowdac Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
248 DAC is used with 32-bit PCI to push a 64-bit address in
249 two cycles. When off all DMA over >4GB is forced through
250 an IOMMU or software bounce buffering.
251 nodac Forbid DAC mode, i.e. DMA >4GB.
252 panic Always panic when IOMMU overflows.
253 calgary Use the Calgary IOMMU if it is available
255 iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
257 swiotlb=<pages>[,force]
258 <pages> Prereserve that many 128K pages for the software IO
260 force Force all IO through the software TLB.
262 Settings for the IBM Calgary hardware IOMMU currently found in IBM
263 pSeries and xSeries machines:
265 calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
266 calgary=[translate_empty_slots]
267 calgary=[disable=<PCI bus number>]
268 panic Always panic when IOMMU overflows
270 64k,...,8M - Set the size of each PCI slot's translation table
271 when using the Calgary IOMMU. This is the size of the translation
272 table itself in main memory. The smallest table, 64k, covers an IO
273 space of 32MB; the largest, 8MB table, can cover an IO space of
274 4GB. Normally the kernel will make the right choice by itself.
276 translate_empty_slots - Enable translation even on slots that have
277 no devices attached to them, in case a device will be hotplugged
280 disable=<PCI bus number> - Disable translation on a given PHB. For
281 example, the built-in graphics adapter resides on the first bridge
282 (PCI bus number 0); if translation (isolation) is enabled on this
283 bridge, X servers that access the hardware directly from user
284 space might stop working. Use this option if you have devices that
285 are accessed from userspace directly on some PCI host bridge.
289 oops=panic Always panic on oopses. Default is to just kill the process,
290 but there is a small probability of deadlocking the machine.
291 This will also cause panics on machine check exceptions.
292 Useful together with panic=30 to trigger a reboot.
294 kstack=N Print N words from the kernel stack in oops dumps.
296 pagefaulttrace Dump all page faults. Only useful for extreme debugging
297 and will create a lot of output.
299 call_trace=[old|both|newfallback|new]
300 old: use old inexact backtracer
301 new: use new exact dwarf2 unwinder
302 both: print entries from both
303 newfallback: use new unwinder but fall back to old if it gets