Re: [PATCH 3/4] kvm tools: Add debug feature to test the IO thread

[Asias He <asias.hejun@gmail.com>]

On 04/20/2011 01:11 AM, Ingo Molnar wrote:
> 
> * Sasha Levin <levinsasha928@gmail.com> wrote:
> 
>> On Tue, 2011-04-19 at 19:52 +0300, Pekka Enberg wrote:
>>> On Mon, Apr 18, 2011 at 4:02 PM, Sasha Levin <levinsasha928@gmail.com> wrote:
>>>> Add --debug-io-delay-cycles and --debug-io-delay-amount to delay the completion of IO requests within virtio-blk.
>>>> This feature allows to verify and debug the threading within virtio-blk.
>>>>
>>>> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
>>>
>>> Well, to be honest, I'm not convinced we need both of these. Isn't
>>> --debug-io-delay=<msec> enough for our use?
>>
>> This came up during our testing.
>>
>> Ingo suggested a large delay so we could easily see the results of
>> threading. The problem we encountered was that having a delay right from
>> the beginning will make the guest kernel take a rather long time to boot
>> and would make actually testing the threading impossible.
>>
>> I've added a delay before the activation of the I/O request completion
>> delay to give the tester/debugger enough time to boot into the guest and
>> prepare anything needed for the test.
>>
>> Making it a constant is also rather hard because different kernels can
>> take a very different amount of I/O requests to boot. Take the simple
>> example of a whether fsck was running during the boot or not.
> 
> I suspect we'll eventually want to have some sort of 'kvm set' subcommand that 
> can modify attributes of running instances? Setting the debug delay would be 
> one of the options:
> 
> 	kvm set MyInstance-1 --debug-io-delay-ms 10000
> 
> That way the delay can be activated in a suitable moment - and disabled again 
> after testing:
> 
> 	kvm set MyInstance-1 --debug-io-delay-ms 0
> 

It's a very good idea.

Do we need:

	kvm get MyInstance-1

which reports all the attributes, or

	kvm get MyInstance-1 --debug-io-delay-ms

which only reports the interested attribute.


-- 
Best Regards,
Asias He