On Fri, Aug 15, 2014 at 10:54:11AM +0530, Amit Shah wrote:
> On (Wed) 13 Aug 2014 [06:00:49], Paul E. McKenney wrote:
> > On Wed, Aug 13, 2014 at 11:14:39AM +0530, Amit Shah wrote:
> > > On (Tue) 12 Aug 2014 [14:41:51], Paul E. McKenney wrote:
> > > > On Tue, Aug 12, 2014 at 02:39:36PM -0700, Paul E. McKenney wrote:
> > > > > On Tue, Aug 12, 2014 at 09:06:21AM -0700, Paul E. McKenney wrote:
> > > > > > On Tue, Aug 12, 2014 at 11:03:21AM +0530, Amit Shah wrote:
> > > > >
> > > > > [ . . . ]
> > > > >
> > > > > > > I know of only virtio-console doing this (via userspace only,
> > > > > > > though).
> > > > > >
> > > > > > As in userspace within the guest? That would not work. The
> > > > > > userspace
> > > > > > that the qemu is running in might. There is a way to extract
> > > > > > ftrace info
> > > > > > from crash dumps, so one approach would be "sendkey alt-sysrq-c",
> > > > > > then
> > > > > > pull the buffer from the resulting dump. For all I know, there
> > > > > > might also
> > > > > > be some script that uses the qemu "x" command to get at the ftrace
> > > > > > buffer.
> > > > > >
> > > > > > Again, I cannot reproduce this, and I have been through the code
> > > > > > several
> > > > > > times over the past few days, and am not seeing it. I could start
> > > > > > sending you random diagnostic patches, but it would be much better
> > > > > > if
> > > > > > we could get the trace data from the failure.
> > >
> > > I think the only recourse I now have is to dump the guest state from
> > > qemu, and attempt to find the ftrace buffers by poking pages and
> > > finding some ftrace-like struct... and then dumping the buffers.
> >
> > The data exists in the qemu guest state, so it would be good to have
> > it one way or another. My current (perhaps self-serving) guess is that
> > you have come up with a way to trick qemu into dropping IPIs.
>
> I didn't get around to doing this yet; will get to it next week.
>
> In the meantime, I tried this on RHEL6 (with RHEL6 qemu and gcc and
> seabios), and that exhibits the problem similarly with my .config.
And I am running my tests successfully on an x86_64 system running
Ubuntu 12.04. Some testing on 14.04 seems to require booting with
acpi=off, leading to my perhaps self-serving guess above.
> <snip>
>
> > > > +
> > > > return true;
> > >
> > > I have return 1; here.
> > >
> > > I'm on linux.git, c8d6637d0497d62093dbba0694c7b3a80b79bfe1.
> >
> > I am working on top of my -rcu tree, which contains the fix from "1" to
> > "true" compared to current mainline. So this will resolve itself, and
> > you should be OK fixing up conflict in either direction.
>
> Yep, I did do that. Just noted here that the hunk didn't directly
> apply.
Fair enough, thank you for letting me know.
Thanx, Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
