Add descriptions of parallel dumping and how to use it.
Signed-off-by: Zhou Wenjian <zhouwj-fnst(a)cn.fujitsu.com>
1.address Baoquan He's comment on disable_cpu_apicid
1.fix some inappropriate description
2.delete some unnecessary description
kexec-kdump-howto.txt | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt
index 05b497f..6e49f35 100644
@@ -616,6 +616,37 @@ options are copied from /proc/cmdline. In general it is best to
command line options using "KDUMP_COMMANDLINE_APPEND=" instead of replacing
the original command line completely.
+Parallel Dumping Operation
+Kexec allows kdump using multiple cpus. So parallel feature can accelerate
+dumping substantially, especially in executing compress and filter.
+ 1."makedumpfile -c --num-threads [THREAD_NUM] /proc/vmcore dumpfile"
+ 2."makedumpfile -c /proc/vmcore dumpfile",
+ 1 has better performance than 2, if THREAD_NUM is larger than two
+ and the usable cpus number is larger than THREAD_NUM.
+Notes on how to use multiple cpus on a capture kernel on x86 system:
+Make sure that you are using a kernel 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.
+You need to specify how many cpus to be used 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.
+You should use necessary and suffcient number of cpus on a capture kernel.
+IOW, don't use too many cpus on a capture kernel, or the capture kernel may
+lead to panic due to Out Of Memory(each cpu uses about 1MB).
+(*) Without disable_cpu_apicid kernel option, capture kernel may lead to
+hang, system reset or power-off at boot, depending on your system and runtime
+situation at the time of crash.
- One can drop into a shell before/after saving vmcore with the help of