On 08/02/16 at 04:49pm, "Zhou, Wenjian/???" wrote: > Hi Baoquan, > > On 08/02/2016 03:46 PM, Baoquan He wrote: > >Hi Wenjian, > > > >On 08/01/16 at 08:23am, Zhou Wenjian wrote: > >>v1->v2: change nr_cpus to maxcpus > >> > >>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 at cn.fujitsu.com> > > > >Discussed with people, it could be better to adjust the > >description about nr_cpus and maxcpus part. I think you can still > >describe nr_cpus/maxcpus in patch 1/2, and keep parallel dumping part in > >2/2. > > > >Originally maxcpus=1 is used for all ARCHes. Later people found > >nr_cpus=1 is better since nr_cpus decides the number of possible cpu > >while maxcpus decides the max working cpu after system boot. So nr_cpus > >can save memory because percpu will pre-allocate memory for each > >possible cpu for hotplug. So on x86 nr_cpus is used because much memory > >can be saved if possible cpu number is very large. > > > >So you can mention that both maxcpus and nr_cpus can be used but nr_cpus > >has advantage if it has been implemented in some ARCHes like x86_64. And > >I guess you mush have tested parallel dumping feature with nr_cpus > >specified, it makes sense to tell people with the real situation. > > > > I think it is better to describe the difference in somewhere else. > Maybe, it's a good choice which just replace maxcpus by maxcpus/nr_cpus. > Then user can choose maxcpus or nr_cpus. > What do you think about it? Putting it in kdump.txt could be better. nr_cpus/maxcpus are normal kernel options, the reason we mentioned them here is crashkernel memory is usually limited, we have to try our best to save memory. So if nr_cpus is available on some ARCHes, we should use it. On x86 nr_cpus=1 has been taken for kdump kernel for a very long time. I think letting people know below things would be good: ~~~~~~~~~~ Firslty both maxcpus and nr_cpus can be used for kdump kernel to specify number of allowed cpu. maxcpus only specify the number of available cpu, while nr_cpus will specify the number of possible cpu which is necessary for hotplug. nr_cpus can be used to limit the amount of percpu memory pre-allocation. And now you just test parallel dumping feature on x86, or more specifically on x86_64. ~~~~~~~~~~~ Thanks Baoquan
