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? -- Thanks Zhou > Thanks > Baoquan > >> --- >> Documentation/kdump/kdump.txt | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt >> index 88ff63d..c5762b7 100644 >> --- a/Documentation/kdump/kdump.txt >> +++ b/Documentation/kdump/kdump.txt >> @@ -394,6 +394,12 @@ Notes on loading the dump-capture kernel: >> dump. Hence generally it is useful either to build a UP dump-capture >> kernel or specify maxcpus=1 option while loading dump-capture kernel. >> >> +* We should bring up a SMP dump-capture kernel if we intend to use 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=[X] and >> + disable_cpu_apic=[Y] 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 >> >> >> > >
