RE: [Xen-devel] debug logging in windows

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> > Is there something similar implemented via hvm/qemu that can log via
hvm
> > log files? That would make life easier. If not, I'll implement it.
> There isn't at the moment, at least not in the xenbits repositories.
> There is one in the XenServer version of qemu, though.  I've attached
> the relevant patch.  If you apply this and rebuild qemu then you
> should be able to send stuff to the qemu logfile by writing bytes to
> port 0x12.  Note that this is rate limited, though, and if you hit the
> limiter the domain will be quite severely punished.

I am using 3.2.1 so it didn't apply for me, but it was more or less what
I was doing anyway, sans the limiter.

One thing I did a little differently was to implement logging on a
per-cpu basis. Eg in my DomU I write to (0x10 + (cpu & 0xf)), and in
qemu I maintain separate buffers for each CPU. This removes the need to
maintain a global lock in the DomU, which is hard in Windows when you
want to log from multiple drivers and call from any IRQL. Without
separating the buffers, I was seeing all sorts of crazy stuff when two
CPU's tried to log at the same time.

I have successfully tracked down the problem anyway I think, I was
simply declaring too much local data in a routine that ran at DIRQL (the
IRQL that hardware interrupts run at), which was (for some reason)
causing a complete hard lockup that not even the debugger could break
into...

I'm now running save+restore in a loop via a script and will see how it
goes...

James

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