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

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Date:	Wed, 3 Aug 2016 10:05:10 +0800
From:	"Zhou, Wenjian/周文剑" 
	<zhouwj-fnst@...fujitsu.com>
To:	Baoquan He <bhe@...hat.com>
CC:	<linux-kernel@...r.kernel.org>, <dyoung@...hat.com>,
	<d.hatayama@...fujitsu.com>, <kexec@...ts.infradead.org>
Subject: Re: [PATCH v3 2/2] Documentation: kdump: add description of bringing
 up SMP dump-capture kernel

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@...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 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
>>
>>
>>
>>
>> _______________________________________________
>> kexec mailing list
>> kexec@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec
>
>

-- 
Thanks
Zhou

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