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

["Zhou, Wenjian/åæå"]

On 08/03/2016 10:18 AM, Baoquan He wrote:
> 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.

I see. I will update the patch.

> > > > +  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@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.infradead.org/mailman/listinfo/kexec
> >
> >
> > --
> > Thanks
> > Zhou


--
Thanks
Zhou