Messages in this thread | | | Date | Mon, 19 Jun 2006 16:30:53 +0900 | From | "Akiyama, Nobuyuki" <> | Subject | Re: [Fastboot] [PATCH] kdump: add a missing notifier before crashing |
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On Fri, 16 Jun 2006 10:37:05 -0600 ebiederm@xmission.com (Eric W. Biederman) wrote:
> > The processing of the notifier is to make a SCSI adaptor power off to > > stop writing in the shared disk completely and then notify to standby-node. > > The kernel has called panic no new SCSI operations were execute. > I'm not saying don't notify your standby-node
As you say, the kernel does not do anything about SCSI operations. But many SCSI adaptors flush their cache after a few seconds pass after a SCSI write command is invoked, especially RAID cards. To completely stop writing immediately, we should make the adaptor power off.
> Please walk me through a real world kernel failure, and show me how > your millisecond requirement is met. > > In the example please answer: > - What causes the kernel to call panic? > - From the real failure to the kernel calling panic how long > does it take?
For instance, if a file system inconsistency is detected, it takes few time until invoking panic. I have seen various kernel failure so far and these will unfortunately occur.
> - What actions does the notifier take to tell the other kernel > it is dead.
The operation is only writing to BMC a few times to use IPMI interface. That operation using outb is very simple.
> - Why do we think the kernel taking that action will be reliable?
I agree the notifier may spoil reliability as compared with doing nothing. It depends on quality of the notifier processing. But I think the one is needed because it is more effective.
> - From the point where we call panic() how long does it take until > the kdump kernel is active?
On my box it takes about one second or so, but on a actual enterprise system which have many disks(hundreds or more) it becomes more.
Thanks,
-- Akiyama, Nobuyuki
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