[PATCH v2] Add checking num-threads of makedumpfile

["Zhou, Wenjian/周文剑"]

On 08/26/2015 04:26 PM, Dave Young wrote:
> On 08/26/15 at 04:18pm, "Zhou, Wenjian/周文剑" wrote:
>> Hello Dave,
>>
>> On 08/26/2015 03:59 PM, Dave Young wrote:
>>> Hi,
>>>
>>> On 08/25/15 at 04:43pm, Zhou Wenjian wrote:
>>>> A new feature that doing compressing and writing by multi-threads
>>>> has been added in makedumpfile. The thread num is specified by
>>>> "--num-threads NUM". According to its implementation, there will
>>>> be performance degradation if the threads are more than cpus.
>>>> So we should check it.
>>>>
>>>> Signed-off-by: Zhou wenjian <zhouwj-fnst at cn.fujitsu.com>
>>>> ---
>>>>   kdumpctl |   15 +++++++++++++++
>>>>   1 files changed, 15 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/kdumpctl b/kdumpctl
>>>> index b504734..fd2abe4 100755
>>>> --- a/kdumpctl
>>>> +++ b/kdumpctl
>>>> @@ -259,6 +259,21 @@ check_config()
>>>>   		esac
>>>>   	done < $KDUMP_CONFIG_FILE
>>>>
>>>> +	grep "^core_collector.*makedumpfile" $KDUMP_CONFIG_FILE | grep -q "num-threads"
>>>> +	if [ $? -eq 0 ];then
>>>> +		local nr_cpus=1
>>>> +		local num_threads=0
>>>> +		local core_collector=`grep "^core_collector" $KDUMP_CONFIG_FILE`
>>>> +
>>>> +		num_threads=`echo ${core_collector#*--num-threads} | awk '{print $1}'`
>>>> +		nr_cpus=`echo ${KDUMP_COMMANDLINE_APPEND#*nr_cpus=} | awk '{print $1}'`
>>>> +
>>>> +		if [ $num_threads -ge $nr_cpus ];then
>>>> +			echo "The num_threads:$num_threads(specified in /etc/kdump.conf) should be less than nr_cpus:$nr_cpus(specified in /etc/sysconfig/kdump)"
>>>> +			echo "or makedumpfile may have bad performance!"
>>>
>>> It is better to do this in makedumpfile source code instead of adding
>>> these warnings specific for num-threads here.
>>>
>>
>> I have one more question.
>> Since multi-thread feature is associated with nr_cpus, should we do something here?
>
> Hmm, adding it in makedumpfile will be too late for warning users. But I do not like
> adding these stuff in distribution script, user should know the limitation if he
> choose the thread number. How about moving it to makedumpfile --help to describe
> the problem just around the num_threads option.
>

Whatever, we should not introduce nr_cpus in makedumpfile --help.
I noticed a discussion between Vivek and Hatayama.
(You can refer to https://lists.fedoraproject.org/pipermail/kexec/2014-March/000687.html)
I think finishing that patch may help.
I will post the patch later.
Please give me some comments on the later patch.

-- 
Thanks
Zhou