On Tue, Dec 01, 2015 at 09:20:02AM +0000, Chris Wilson wrote:
> On Tue, Dec 01, 2015 at 10:13:10AM +0100, Daniel Vetter wrote:
> > On Tue, Dec 01, 2015 at 09:04:23AM +0000, Chris Wilson wrote:
> > > On Tue, Dec 01, 2015 at 09:28:08AM +0100, Daniel Vetter wrote:
> > > > On Mon, Nov 30, 2015 at 10:11:12AM +0000, Chris Wilson wrote:
> > > > > On Thu, Nov 26, 2015 at 12:34:34PM +0100, Daniel Vetter wrote:
> > > > > > So there's 3 competing proposals for what wait_ioctl should do wrt
> > > > > > -EIO:
> > > > > >
> > > > > > - return -EIO when the gpu is wedged. Not terribly useful for
> > > > > > userspace since it might race with a hang and then there's no
> > > > > > guarantee that a subsequent execbuf won't end up in an -EIO.
> > > > > > Terminally wedge really can only be reliably signalled at execbuf
> > > > > > time, and userspace needs to cope with that (or decide not to
> > > > > > bother).
> > > > > >
> > > > > > - EIO for any obj that suffered from a reset. This means big internal
> > > > > > reorginazation in the kernel since currently we track reset stats
> > > > > > per-ctx and not on the obj. That's also what arb robustness wants.
> > > > > > We could do this, but this feels like new ABI territory with the
> > > > > > usual userspace requirements and high hurdles.
> > > > > >
> > > > > > - No -EIO at all. Consistent with set_domain_ioctl and simplest to
> > > > > > implement. Which is what this patch does.
> > > > >
> > > > > Since no one else is weighing into the ABI discussion, I'm happy with
> > > > > losing EIO here. I thought it could be useful, but as no one is using or
> > > > > seems likely to start using it, begone.
> > > > >
> > > > > > We can always opt to change this later on if there's a real need.
> > > > > >
> > > > > > To make the test really exercise this do a full wedged gpu hang, to
> > > > > > make sure -EIO doesn't leak out at all.
> > > > > >
> > > > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > > > > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > > > > > ---
> > > > > > tests/gem_eio.c | 6 +++++-
> > > > > > 1 file changed, 5 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/tests/gem_eio.c b/tests/gem_eio.c
> > > > > > index a24c8f1c53b5..8345d1a7a429 100644
> > > > > > --- a/tests/gem_eio.c
> > > > > > +++ b/tests/gem_eio.c
> > > > > > @@ -161,10 +161,14 @@ static void test_wait(int fd)
> > > > > > {
> > > > > > igt_hang_ring_t hang;
> > > > > >
> > > > > > + igt_require(i915_reset_control(false));
> > > > >
> > > > > However, this is not required to test the ABI change above as the wait
> > > > > itself will still hang, whether or not it wedges the GPU.
> > > >
> > > > Yes it's not strictly required, but without it the testcase is fairly
> > > > boring. If we move the check_wedge out of wait_request then a normail gpu
> > > > reset would always return 0 (after retrying a few times perhaps), so I
> > > > figured testing the wedged case is the only one that's worth it.
> > >
> > > But wedging during the hang is also not interesting as we have no
> > > opportunity to see the reset failure in the test case. Putting the GPU
> > > into the wedged state before the wait, should be a trivial test that the
> > > object is idle after the reset.
> >
> > Right now (with current kernels) we see an -EIO with this testcase instead
> > of 0 in the wait. Without disabling reset we see 0 both on fixed and
> > broken kernels. So I don't really see why not testing this case is a good
> > idea? It's the one we're currently failing at and leak -EIO to userspace.
>
> Because that wasn't the ABI I was trying to test here and expected to
> maintain! I was just aiming for covering the ioctl calls with expected
> EIO (to do the opposite would need something like trinity or a guided
> fuzzer).
Well yeah, but I thought we decided to change it? So Ack or not?
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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