[PATCH 1/2] Documentation: kdump: update maxcpus to nr_cpus

[PATCH 1/2] Documentation: kdump: update maxcpus to nr_cpus

[Zhou Wenjian]

Parameter nr_cpus is used to bring up a SMP dump-capture kernel,
instead of the old parameter maxcpus. This commit update it in
Documentation/kdump/kdump.txt.

Signed-off-by: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>
---
 Documentation/kdump/kdump.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 88ff63d..9a77247 100644
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -392,7 +392,7 @@ Notes on loading the dump-capture kernel:
 
 * We generally don' have to bring up a SMP kernel just to capture the
   dump. Hence generally it is useful either to build a UP dump-capture
-  kernel or specify maxcpus=1 option while loading dump-capture kernel.
+  kernel or specify nr_cpus=1 option while loading dump-capture kernel.
 
 * For s390x there are two kdump modes: If a ELF header is specified with
   the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
-- 
1.8.3.1

[PATCH 2/2] Documentation: kdump: add description of bringing up SMP dump-capture kernel

[Zhou Wenjian]

SMP dump-capture kernel is useful to improve the performance of kdump in
some cases. So add the description of bringing up SMP dump-capture kernel.

Signed-off-by: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>
---
 Documentation/kdump/kdump.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 9a77247..155a63c 100644
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -394,6 +394,12 @@ Notes on loading the dump-capture kernel:
   dump. Hence generally it is useful either to build a UP dump-capture
   kernel or specify nr_cpus=1 option while loading dump-capture kernel.
 
+* We should bring up a SMP dump-capture kernel if we intend to use multi-threads
+  programs with it, such as parallel dump feature of makedumpfile. Otherwise,
+  the multi-threads program may have a great performance degradation.
+  To bring up a SMP dump-capture kernel, we should specify nr_cpus=[X] and
+  disable_cpu_apic=[Y] options while loading it.
+
 * For s390x there are two kdump modes: If a ELF header is specified with
   the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
   is done on all other architectures. If no elfcorehdr= kernel parameter is
-- 
1.8.3.1

Re: [PATCH 1/2] Documentation: kdump: update maxcpus to nr_cpus

[Baoquan He]

On 07/29/16 at 11:23am, Zhou Wenjian wrote:
> Parameter nr_cpus is used to bring up a SMP dump-capture kernel,
> instead of the old parameter maxcpus. This commit update it in
> Documentation/kdump/kdump.txt.
> 
> Signed-off-by: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>
> ---
>  Documentation/kdump/kdump.txt | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index 88ff63d..9a77247 100644
> --- a/Documentation/kdump/kdump.txt
> +++ b/Documentation/kdump/kdump.txt
> @@ -392,7 +392,7 @@ Notes on loading the dump-capture kernel:
>  
>  * We generally don' have to bring up a SMP kernel just to capture the
>    dump. Hence generally it is useful either to build a UP dump-capture
> -  kernel or specify maxcpus=1 option while loading dump-capture kernel.
> +  kernel or specify nr_cpus=1 option while loading dump-capture kernel.


IIRC, ARCHes like ppc don't have nr_cpus yet, maxpcus is necessary. So
either you explicitly tell which can use nr_cpus and which can only use
maxcpus option, or drop this patch for now.

>  
>  * For s390x there are two kdump modes: If a ELF header is specified with
>    the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
> -- 
> 1.8.3.1
> 
> 
>