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

[Sasha Levin <levinsasha928@gmail.com>]

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.

-- 

Sasha.