Re: [PATCH v3 2/2] Documentation: kdump: add description of bringing up SMP dump-capture kernel

From: "Zhou, Wenjian/åæå"
Date: Tue Aug 02 2016 - 22:06:38 EST


On 08/03/2016 09:58 AM, Baoquan He wrote:
On 08/03/16 at 08:59am, Zhou Wenjian wrote:
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@xxxxxxxxxxxxxx>
---
Documentation/kdump/kdump.txt | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 4aa194e..948b42d 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 bring up a SMP dump-capture kernel if we intend to use

Well, here about SMP dump-capture kernel do you mean kdump kernel with
multi-cpu? If I understand it correctly, it's still SMP kdump kernel
though nr_cpus=1 is specified.


Actually, I haven't know the detail about it. I wrote the sentence almost
based on the original description:

* 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.

+ 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 maxcpus\nr_cpus and 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




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--
Thanks
Zhou