From: "Yu, Fenghua" <fenghua.yu@xxxxxxxxx> Subject: RE: [PATCH v1 0/2] x86, apic: Disable BSP if boot cpu is AP Date: Tue, 16 Oct 2012 04:51:36 +0000 >> -----Original Message----- >> From: HATAYAMA Daisuke [mailto:d.hatayama at jp.fujitsu.com] >> Sent: Monday, October 15, 2012 9:35 PM >> To: linux-kernel at vger.kernel.org; kexec at lists.infradead.org; >> x86 at kernel.org >> Cc: mingo at elte.hu; tglx at linutronix.de; hpa at zytor.com; Brown, Len; Yu, >> Fenghua; vgoyal at redhat.com; ebiederm at xmission.com; >> grant.likely at secretlab.ca; rob.herring at calxeda.com; >> d.hatayama at 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. > Hello Fenghua. I've of course noticed your patch set and locally tested, but I saw NMI to BSP failed in the 2nd kernel. I'll send a log to you later. BTW, I tested with your previous v8 patch set. Did you change something during v8 to v9 relevant to this issue? Thanks. HATAYAMA, Daisuke
