[Mesa-dev] [PATCH] i965: Perform manual preemption checks between commands

[Rafael Antognolli]

On Tue, Mar 05, 2019 at 07:50:24PM +0000, Chris Wilson wrote:
> Quoting Rafael Antognolli (2019-03-05 19:33:03)
> > On Tue, Mar 05, 2019 at 09:40:20AM +0000, Chris Wilson wrote:
> > > Not all commands support being preempted as they execute, and for those
> > > make sure we at least check for being preempted before we start so as to
> > > try and minimise the latency of whomever is more important than
> > > ourselves.
> > > 
> > > Cc: Jari Tahvanainen <jari.tahvanainen at intel.com>,
> > > Cc: Rafael Antognolli <rafael.antognolli at intel.com>
> > > Cc: Kenneth Graunke <kenneth at whitecape.org>
> > > ---
> > > Always double check before you hit send.
> > > ---
> > >  src/mesa/drivers/dri/i965/brw_defines.h | 1 +
> > >  src/mesa/drivers/dri/i965/brw_draw.c    | 7 +++++++
> > >  2 files changed, 8 insertions(+)
> > > 
> > > diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
> > > index 2729a54e144..ef71c556cca 100644
> > > --- a/src/mesa/drivers/dri/i965/brw_defines.h
> > > +++ b/src/mesa/drivers/dri/i965/brw_defines.h
> > > @@ -1420,6 +1420,7 @@ enum brw_pixel_shader_coverage_mask_mode {
> > >  
> > >  #define MI_NOOP                              (CMD_MI | 0)
> > >  
> > > +#define MI_ARB_CHECK                 (CMD_MI | 0x5 << 23)
> > >  #define MI_BATCH_BUFFER_END          (CMD_MI | 0xA << 23)
> > >  
> > >  #define MI_FLUSH                     (CMD_MI | (4 << 23))
> > > diff --git a/src/mesa/drivers/dri/i965/brw_draw.c b/src/mesa/drivers/dri/i965/brw_draw.c
> > > index d07349419cc..a04e334ffc4 100644
> > > --- a/src/mesa/drivers/dri/i965/brw_draw.c
> > > +++ b/src/mesa/drivers/dri/i965/brw_draw.c
> > > @@ -196,6 +196,13 @@ brw_emit_prim(struct brw_context *brw,
> > >     if (verts_per_instance == 0 && !prim->is_indirect && !xfb_obj)
> > >        return;
> > >  
> > > +   /* If this object is not itself preemptible, check before we begin. */
> > > +   if (!brw->object_preemption) {
> > > +      BEGIN_BATCH(1);
> > > +      OUT_BATCH(MI_ARB_CHECK);
> > > +      ADVANCE_BATCH();
> > > +   }
> > > +
> > 
> > "The command streamer will preempt in the case arbitration is enabled,
> > there is a pending execution list and this command is currently being
> > parsed."
> > 
> > If there is a pending execution list, shouldn't we have been preempted
> > already, since mid-batch preemption is supposed to be enabled?
> 
> No, it still only occurs on certain instructions, not every instruction
> boundary.

Sounds good. In that case,

Reviewed-by: Rafael Antognolli <rafael.antognolli at intel.com>

> -Chris
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