* Sasha Levin <levinsasha...@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 <levinsasha...@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 <levinsasha...@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
?
Thanks,
Ingo
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