> -----Original Message----- > From: HATAYAMA Daisuke [mailto:d.hatayama@jp.fujitsu.com] > Sent: Monday, October 15, 2012 9:35 PM > To: linux-kernel@vger.kernel.org; kexec@lists.infradead.org; > x86@kernel.org > Cc: mingo@elte.hu; tglx@linutronix.de; hpa@zytor.com; Brown, Len; Yu, > Fenghua; vgoyal@redhat.com; ebiederm@xmission.com; > grant.likely@secretlab.ca; rob.herring@calxeda.com; > d.hatayama@jp.fujitsu.com > Subject: [PATCH v1 0/2] x86, apic: Disable BSP if boot cpu is AP > > Multiple CPUs are useful for CPU-bound processing like compression and > I do want to use compression to generate crash dump quickly. But now > we cannot wakeup the 2nd and later cpus in the kdump 2nd kernel if > crash happens on AP. If crash happens on AP, kexec enters the 2nd > kernel with the AP, and there BSP in the 1st kernel is expected to be > haling in the 1st kernel or possibly in any fatal system error state. > > To wake up AP, we use the method called INIT-INIT-SIPI. INIT causes > BSP to jump into BIOS init code. A typical visible behaviour is hang > or immediate reset, depending on the BIOS init code. > > AP can be initiated by INIT even in a fatal state: MP spec explains > that processor-specific INIT can be used to recover AP from a fatal > system error. On the other hand, there's no method for BSP to recover; > it might be possible to do so by NMI plus any hand-coded reset code > that is carefully designed, but at least I have no idea in this > direction now. In my BSP hotplug patchset, BPS is waken up by NMI. The patchset is not in tip tree yet. BSP hotplug patchset can be found at https://lkml.org/lkml/2012/10/12/336 > > Therefore, the idea I do in this patch set is simply to disable BSP if > vboot cpu is AP. > The BSP hotplug patchset will be useful for you goal. With the BSP hotplug patcheset, you can wake up BSP and don't need to disable it. > My motivation is to use multiple CPUs in order to quickly generate > crash dump on the machine with huge amount of memory. I assume such > machine tends to also have a lot of CPUs. So disabling one CPU would > be no problem. Luckily you don't need to disable any CPU to archive your goal with the BSP hotplug pachest:) On a dual core/single thread machine, this means you get 100% performance boost with BSP's help. Plus crash dump kernel code is better structured by not treating BSP specially. Thanks. -Fenghua {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I