OS support for fault tolerance
jrisom at gmail.com
Tue Feb 14 17:38:47 UTC 2012
On 2/14/2012 10:57 AM, Julian Elischer wrote:
> On 2/14/12 6:23 AM, Maninya M wrote:
>> For multicore desktop computers, suppose one of the cores fails, the
>> FreeBSD OS crashes. My question is about how I can make the OS tolerate
>> this hardware fault.
>> The strategy is to checkpoint the state of each core at specific
>> of time in main memory. Once a core fails, its previous state is
>> from the main memory, and the processes that were running on it are
>> rescheduled on the remaining cores.
>> I read that the OS tolerates faults in large servers. I need to make
>> it do
>> this for a Desktop OS. I assume I would have to change the scheduler
>> program. I am using FreeBSD 9.0 on an Intel core i5 quad core machine.
>> How do I go about doing this? What exactly do I need to save for the
>> "state" of the core? What else do I need to know?
>> I have absolutely no experience with kernel programming or with FreeBSD.
>> Any pointers to good sources about modifying the source-code of FreeBSD
>> would be greatly appreciated.
> This question has always intrigued me, because I'm always amazed
> that people actually try.
> From my viewpoint, There's really not much you can do if the core
> that is currently holding the scheduler lock fails.
> And what do you mean by 'fails"? do you run constant diagnostics?
> how do you tell when it is failed? It'd be hard to detect that 'multiply'
> has suddenly started giving bad results now and then.
> if it just "stops" then you might be able to have a watchdog that
> notices, but what do you do when it was half way through rearranging
> a list of items? First, you have to find out that it held
> the lock for the module and then you have to find out what it had
> done and clean up the mess.
> This requires rewriting many many parts of the kernel to remove
> 'transient inconsistent states". and even then, what do you do if it
> was half way through manipulating some hardware..
> and when you've figured that all out, how do you cope with the
> mess it made because it was dying?
> Say for example it had started calculating bad memory offsets
> before writing out some stuff and written data out over random memory?
> but I'm interested in any answers people may have
The only way I could see that it could be done, without direct hardware
support, would be to virtualize it similar to how valgrind works.
You'll take a speed hit bad enough to want to turn it off, but it could
be possible. Testing that it works well could just mean overclocking
your cpu until it starts crashing, and then seeing if it doesn't crash.
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