[PATCH v4 1/2] Documentation: kdump: remind user of nr_cpus

[PATCH v4 1/2] Documentation: kdump: remind user of nr_cpus

[Zhou Wenjian]

v3->v4: update the description of bring up SMP dump-capture kernel
v2->v3: add description of nr_cpus.
v1->v2: change nr_cpus to maxcpus

nr_cpus can help to save memory. So we should remind user of it.

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

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 88ff63d..b474060 100644
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -393,6 +393,8 @@ 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.
+  Note, though maxcpus always works, we should replace it by nr_cpus to
+  save memory if supported by the current ARCH, such as x86.
 
 * 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 v4 2/2] Documentation: kdump: add description of enable multi-cpus support

[Zhou Wenjian]

multi-cpus support is useful to improve the performance of kdump in
some cases. So add the description of enable multi-cpus support in
dump-capture kernel.

Signed-off-by: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>
---
 Documentation/kdump/kdump.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index b474060..028cf26 100644
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -396,6 +396,13 @@ Notes on loading the dump-capture kernel:
   Note, though maxcpus always works, we should replace it by nr_cpus to
   save memory if supported by the current ARCH, such as x86.
 
+* We should enable multi-cpus support in 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 enable multi-cpus support, we should bring up
+  a SMP dump-capture kernel and specify maxcpus\nr_cpus, disable_cpu_apic=[X]
+  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 v4 1/2] Documentation: kdump: remind user of nr_cpus

[Baoquan He]

Hi Wenjian,

On 08/03/16 at 10:31am, Zhou Wenjian wrote:
> v3->v4: update the description of bring up SMP dump-capture kernel
> v2->v3: add description of nr_cpus.
> v1->v2: change nr_cpus to maxcpus
> 
> nr_cpus can help to save memory. So we should remind user of it.
> 
> Signed-off-by: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>

The change log can be put in cover-letter if you are posting a patchset,
or put it below the three dashes where it will be discarded
automatically when maintainer apply your patch to his/her branch.

Next time please CC akpm too, he helps to pick up these kexec related
patches.

Except for this, I am fine with this patchset. Ack it again.

Acked-by: Baoquan He <bhe@redhat.com>

Thanks
Baoquan

> ---
>  Documentation/kdump/kdump.txt | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index 88ff63d..b474060 100644
> --- a/Documentation/kdump/kdump.txt
> +++ b/Documentation/kdump/kdump.txt
> @@ -393,6 +393,8 @@ 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.
> +  Note, though maxcpus always works, we should replace it by nr_cpus to
> +  save memory if supported by the current ARCH, such as x86.
>  
>  * 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
> 
> 
> 
> 
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