On Mon, Apr 2, 2012 at 1:52 PM, Daniel Vetter <daniel at ffwll.ch> wrote: > On Mon, Apr 02, 2012 at 01:45:39PM -0700, Andrew Lutomirski wrote: >> On Mon, Apr 2, 2012 at 11:48 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: >> > Inspired by the recent ppgtt regression report, where switching of >> > dmar only for the gpu seems to fix things completely, I've looked >> > again at the semaphores+vt-d situation. >> > >> > Contrary to my earlier testing a few months back my system is now >> > stable with dmar disabled for the igd, and not only when disabling >> > dmar completely. >> > >> > So I'm rather hopeful that all our recent fixes for snb have changed >> > things for code and it's time to try enabling semaphores again. We've >> > also had issues with enabling semaphores which are not vt-d related, >> > but I guess these are all fixed by the autoreport-disabling and lazy >> > request fix. And there's only one way to find out whether there are >> > still other issues ... >> > >> > Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch> >> > >> > --- >> > >> > If no further vt-d regressions show up in the 3.4 cycle I plan to >> > merge this into -next for 3.5 (in a month or so). Comments about how >> > unfeasibly you deem this highly welcome. >> > -Daniel >> > --- >> > ?drivers/gpu/drm/i915/i915_gem_execbuffer.c | ? ?8 +++++--- >> > ?1 files changed, 5 insertions(+), 3 deletions(-) >> > >> > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c >> > index 8e0b686..ac52433 100644 >> > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c >> > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c >> > @@ -849,9 +849,11 @@ intel_enable_semaphores(struct drm_device *dev) >> > ? ? ? ?if (i915_semaphores >= 0) >> > ? ? ? ? ? ? ? ?return i915_semaphores; >> > >> > - ? ? ? /* Disable semaphores on SNB */ >> > - ? ? ? if (INTEL_INFO(dev)->gen == 6) >> > - ? ? ? ? ? ? ? return 0; >> > +#ifdef CONFIG_INTEL_IOMMU >> > + ? ? ? /* Disable semaphores on SNB if VT-d is on. */ >> > + ? ? ? if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped) >> > + ? ? ? ? ? ? ? return false; >> >> It might be nice to have a printk here giving instructions for how to work >> around this. ?For example: >> >> i915: Disabling semaphores to work around a DMAR issue. ?As an >> alternative, boot with intel_iommu=igfx_off [or on, igfx_off, or >> whatever it's supposed to be]. >> >> The documentation in kernel-parameters.txt is at best unclear to the >> uninitiated. > > If this really does work, I'll look into this. Atm it's still unclear > where to exactly put the plain, we need to annoy internal hardware people > to analyze this. Once we have enough evidence that the combination of gpu > with various features enable plus VT-d just doesn't seem to work reliably. > > So can you check whether things do indeed work with this patch, atop > kernel 3.4-rc1? Iirc you've been the one with the most trouble when > semaphores are enabled ... I've had a hard time reproducing the problems lately. The unconditional instant hard hang went away a few months ago, I think. I'll give it another shot when I get home to that machine. --Andy
