[igt-dev] [Intel-gfx] [PATCH i-g-t 3/3] igt: Use COND_BBEND for busy spinning on gen9

[Chris Wilson]

Quoting Chris Wilson (2019-11-13 18:42:06)
> Quoting Chris Wilson (2019-11-13 18:28:08)
> > From: Jon Bloomfield <jon.bloomfield at intel.com>
> > 
> > gen9+ introduces a cmdparser for the BLT engine which copies the
> > incoming BB to a kmd owned buffer for submission (to prevent changes
> > being made after the bb has been safely scanned). This breaks the
> > spin functionality because it relies on changing the submitted spin
> > buffers in order to terminate them.
> > 
> > Instead, for gen9+, we change the semantics by introducing a COND_BB_END
> > into the infinite loop, to wait until a memory flag (in anothe bo) is
> > cleared.
> > 
> > v2: Correct nop length to avoid overwriting bb_end instr when using
> >     a dependency bo (cork)
> > v3: fix conflicts on igt_dummyload (Mika)
> > v4: s/bool running/uint32_t running, fix r->delta (Mika)
> > v5: remove overzealous assert (Mika)
> > v6: rebase on top of lib changes (Mika)
> > v7: rework on top of public igt lib changes (Mika)
> > v8: rebase
> > v9: simplify by using bb end as conditional (Chris)
> > 
> > Signed-off-by: Jon Bloomfield <jon.bloomfield at intel.com> (v2)
> > Cc: Joonas Lahtinen <joonas.lahtinen at intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> > Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > ---
> >  lib/i830_reg.h                          |  2 +-
> >  lib/igt_dummyload.c                     | 17 ++++++++++++++++-
> >  lib/intel_reg.h                         |  3 +++
> >  tests/i915/gem_double_irq_loop.c        |  2 --
> >  tests/i915/gem_write_read_ring_switch.c |  2 +-
> >  5 files changed, 21 insertions(+), 5 deletions(-)
> > 
> > diff --git a/lib/i830_reg.h b/lib/i830_reg.h
> > index a57691c7e..410202567 100644
> > --- a/lib/i830_reg.h
> > +++ b/lib/i830_reg.h
> > @@ -43,7 +43,7 @@
> >  /* broadwater flush bits */
> >  #define BRW_MI_GLOBAL_SNAPSHOT_RESET   (1 << 3)
> >  
> > -#define MI_COND_BATCH_BUFFER_END       (0x36<<23 | 1)
> > +#define MI_COND_BATCH_BUFFER_END       (0x36 << 23)
> >  #define MI_DO_COMPARE                  (1<<21)
> >  
> >  #define MI_BATCH_BUFFER_END    (0xA << 23)
> > diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> > index c079bd045..652d469a0 100644
> > --- a/lib/igt_dummyload.c
> > +++ b/lib/igt_dummyload.c
> > @@ -208,7 +208,22 @@ emit_recursive_batch(igt_spin_t *spin,
> >          * trouble. See https://bugs.freedesktop.org/show_bug.cgi?id=102262
> >          */
> >         if (!(opts->flags & IGT_SPIN_FAST))
> > -               cs += 1000;
> > +               cs += 960;
> > +
> > +       if (gen >= 8) {
> 
> If we push this back to gen>7 it will allow us to use it with its
> cmdparser as well.
> 
> Hmm? I guess we could just do gen>6 so that there's some systematic
> cutoff point.

Oh, well, it appears the magic compare mode doesn't exist until Skylake.
Fortunately, it exists!
-Chris