Add notes on how to use multiple cpus on x86 system. That is, these
are about two kernel options, disable_cpus_apicid and nr_cpus.
I also wrote note on memory consumption issue about nr_cpus option.
In the notes, I kept x86 hardware issue just a little in order to
avoid too detailed description.
I didn't write any concrete example on makedumpfile usage for parallel
processing since we have not decided official way on kexec-tools.
Signed-off-by: HATAYAMA Daisuke <d.hatayama(a)jp.fujitsu.com>
---
kexec-kdump-howto.txt | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt
index 7ffeab9..3600ec4 100644
--- a/kexec-kdump-howto.txt
+++ b/kexec-kdump-howto.txt
@@ -537,6 +537,39 @@ dump data from stdard input to a normal dumpfile (readable with
analysis
tools).
For example: "makedumpfile -R vmcore < vmcore.flat"
+Notes on how to use multiple cpus on a capture kernel on x86 system
+
+To use multiple cpus on a capture kernel on x86 system:
+
+- First, confirm that you are using a sufficiently new kernel version
+ that supports disable_cpu_apicid kernel option as a capture kernel,
+ which is needed to avoid x86 specific hardware issue (*). The
+ disable_cpu_apicid kernel option is automatically appended by
+ kdumpctl script and is ignored if the kernel doesn't support
+ it. Thus, you don't need to do anything else except for the
+ confirmation.
+
+- Then, you need to specify how many cpus you use in a capture kernel
+ by specifying the number of cpus in nr_cpus kernel option in
+ /etc/sysconfig/kdump. nr_cpus is 1 at default.
+
+Note strongly that you should use necessary and sufficnet amount of
+cpus on a capture kernel. IOW, don't use too many cpus on a capture
+kernel, or the capture kernel easily leads to panic due to Out Of
+Memory.
+
+There are kernel data structures and drivers allocating memory in
+proportion to the number of cpus. More you use cpus, more and more
+memory system consumes. Memory is rare, limited resource in a capture
+kernel. Reserved memory should be kept as less as possible. When
+configuring nr_cpus option, you should confirm that kdump certainly
+successfully works without leading to panic due to Out Of Memory on a
+capture kernel.
+
+(*) Without disable_cpu_apicid kernel option, capture kernel leads to
+hang, system reset or power-off at boot, depending on your system and
+runtime situation at the time of crash.
+
Caveats:
Console frame-buffers and X are not properly supported. If you typically run
--
1.8.5.3
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