[PATCH V4] kexec-kdump-howto:Add introduction of parallel dumping

[Zhou Wenjian]

Add descriptions of parallel dumping and how to use it.

Signed-off-by: Zhou Wenjian 
---
v3->v4:
    1.fix some wrong words
v2->v3:
    1.address Baoquan He's comment on disable_cpu_apicid
v1->v2:
    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..b4cdc22 100644
--- a/kexec-kdump-howto.txt
+++ b/kexec-kdump-howto.txt
@@ -616,6 +616,37 @@ options are copied from /proc/cmdline. In general it is best to append
 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 compression and filter.
+For example:
+
+	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 sufficient number of cpus on a capture kernel.
+Warning: Don't use too many cpus on a capture kernel, or the capture kernel
+may lead to panic due to Out Of Memory.
+
+(*) 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.
+
 Debugging Tips
 --------------
 - One can drop into a shell before/after saving vmcore with the help of

[Dave Young]

On 09/25/15 at 04:19pm, Zhou Wenjian wrote:
> Add descriptions of parallel dumping and how to use it.
> Signed-off-by: Zhou Wenjian
>
> v3->v4:
>    1.fix some wrong words
> v2->v3:
>    1.address Baoquan He's comment on disable_cpu_apicid
> v1->v2:
>    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..b4cdc22 100644
> --- a/kexec-kdump-howto.txt
> +++ b/kexec-kdump-howto.txt
> @@ -616,6 +616,37 @@ options are copied from /proc/cmdline. In general it is best to append
>  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 compression and filter.
> +For example:
> 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 sufficient number of cpus on a capture kernel.
> +Warning: Don't use too many cpus on a capture kernel, or the capture kernel
> +may lead to panic due to Out Of Memory.
>
> +(*) 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.
> Debugging Tips
> One can drop into a shell before/after saving vmcore with the help of
>
> -- 
> 1.8.3.1
>
> kexec mailing list
> [e-mail]
> https://lists.fedoraproject.org/mailman/listinfo/kexec

Thanks for the update.

Acked-by: Dave Young

[Pratyush Anand]

On 25/09/2015:04:19:44 PM, Zhou Wenjian wrote:
> Add descriptions of parallel dumping and how to use it.
>
> Signed-off-by: Zhou Wenjian

Reviewed-by: Pratyush Anand