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

[Baoquan He]

On 08/03/16 at 10:05am, "Zhou, Wenjian/åæå" wrote:
> 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.

This is right. Here it means either you build a UP kernel used for kdump
kernel because kdump kernel doesn't have to be the same as the 1st
kernel, or you use smp kernel with maxcpus=1 specified. So if you want
to say kdump kernel with multi-cpu need be brought up to improve the
performance of parallel dumping, you need point it out clearly.

> 
> >>+  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
> 
>