On Wed, May 26, 2021 at 06:34:44PM -0700, Daniele Ceraolo Spurio wrote:
>
>
> On 5/26/2021 12:11 PM, Matthew Brost wrote:
> > With virtual engines, it is no longer possible to know which specific
> > physical engine a given request will be executed on at the time that
> > request is generated. This means that the request itself must be engine
> > agnostic - any direct register writes must be relative to the engine
> > and not absolute addresses.
> >
> > The LRI command has support for engine relative addressing. However,
> > the mechanism is not transparent to the driver. The scheme for Gen11
> > (MI_LRI_ADD_CS_MMIO_START) requires the LRI address to have no
> > absolute engine base component in the ring and BBs. The hardware then
> > adds on the correct engine offset at execution time. This differs
> > slightly for LRC where the upper bits of the base component are just
> > ignored.
> >
> > Due to the non-trivial and differing schemes on different hardware, it
> > is not possible to simply update the code that creates the LRI
> > commands to set a remap flag and let the hardware get on with it.
> > Instead, this patch adds function wrappers for generating the LRI
> > command itself and then for constructing the correct address to use
> > with the LRI.
> >
> > Bspec: 45606
> > Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > CC: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> > CC: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > CC: Chris P Wilson <chris.p.wilson@xxxxxxxxx>
> > CC: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gem/i915_gem_context.c | 7 ++++---
> > drivers/gpu/drm/i915/gt/intel_engine_cs.c | 22 ++++++++++++++++++++
> > drivers/gpu/drm/i915/gt/intel_engine_types.h | 3 +++
> > drivers/gpu/drm/i915/gt/intel_gpu_commands.h | 6 ++++++
> > drivers/gpu/drm/i915/gt/intel_lrc.c | 4 +---
> > 5 files changed, 36 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > index 188dee13e017..a8a195bfcb57 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > @@ -1211,7 +1211,7 @@ static int emit_ppgtt_update(struct i915_request *rq, void *data)
> > {
> > struct i915_address_space *vm = rq->context->vm;
> > struct intel_engine_cs *engine = rq->engine;
> > - u32 base = engine->mmio_base;
> > + u32 base = engine->lri_mmio_base;
> > u32 *cs;
> > int i;
> > @@ -1223,7 +1223,7 @@ static int emit_ppgtt_update(struct i915_request *rq, void *data)
> > if (IS_ERR(cs))
> > return PTR_ERR(cs);
> > - *cs++ = MI_LOAD_REGISTER_IMM(2);
> > + *cs++ = MI_LOAD_REGISTER_IMM_REL(engine, 2);
>
> This is the only place where you changed the behavior and I think it is
> going away
> (https://lists.freedesktop.org/archives/dri-devel/2021-May/305328.html), so
> the new macro is potentially not needed.
>
See my last comment, I think this irrelevant as I think I missed some
cases where this macro should be used.
> > *cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_UDW(base, 0));
> > *cs++ = upper_32_bits(pd_daddr);
> > @@ -1245,7 +1245,8 @@ static int emit_ppgtt_update(struct i915_request *rq, void *data)
> > if (IS_ERR(cs))
> > return PTR_ERR(cs);
> > - *cs++ = MI_LOAD_REGISTER_IMM(2 * GEN8_3LVL_PDPES) | MI_LRI_FORCE_POSTED;
> > + *cs++ = MI_LOAD_REGISTER_IMM_REL(engine, 2 * GEN8_3LVL_PDPES) |
> > + MI_LRI_FORCE_POSTED;
> > for (i = GEN8_3LVL_PDPES; i--; ) {
> > const dma_addr_t pd_daddr = i915_page_dir_dma_addr(ppgtt, i);
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > index 3f9a811eb02b..0de6bc533776 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > @@ -15,6 +15,7 @@
> > #include "intel_engine_pm.h"
> > #include "intel_engine_user.h"
> > #include "intel_execlists_submission.h"
> > +#include "intel_gpu_commands.h"
> > #include "intel_gt.h"
> > #include "intel_gt_requests.h"
> > #include "intel_gt_pm.h"
> > @@ -222,6 +223,25 @@ static u32 __engine_mmio_base(struct drm_i915_private *i915,
> > return bases[i].base;
> > }
> > +static bool i915_engine_has_relative_lri(const struct intel_engine_cs *engine)
> > +{
> > + if (INTEL_GEN(engine->i915) < 11)
> > + return false;
> > +
> > + return true;
>
> We already have intel_engine_has_relative_mmio(), can just re-use that. Note
> that I915_ENGINE_HAS_RELATIVE_MMIO is only set for gen12+ at the moment;
> this was because CI failed on ICL and since we urgently needed the change
> for gen12 we just excluded gen11 and pushed (see Mika's comment @
> https://lists.freedesktop.org/archives/intel-gfx/2019-September/211812.html).
> It should be ok to extend that to gen11 if we get a green CI.
>
Let me send out a trybot with intel_engine_has_relative_mmio with this
enabled for gen11.
> > +}
> > +
> > +static void lri_init(struct intel_engine_cs *engine)
> > +{
> > + if (i915_engine_has_relative_lri(engine)) {
> > + engine->lri_cmd_mode = MI_LRI_LRM_CS_MMIO;
> > + engine->lri_mmio_base = 0;
> > + } else {
> > + engine->lri_cmd_mode = 0;
> > + engine->lri_mmio_base = engine->mmio_base;
> > + }
> > +}
> > +
> > static void __sprint_engine_name(struct intel_engine_cs *engine)
> > {
> > /*
> > @@ -329,6 +349,8 @@ static int intel_engine_setup(struct intel_gt *gt, enum intel_engine_id id)
> > /* Nothing to do here, execute in order of dependencies */
> > engine->schedule = NULL;
> > + lri_init(engine);
> > +
> > ewma__engine_latency_init(&engine->latency);
> > seqcount_init(&engine->stats.lock);
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > index 9ef349cd5cea..e48da23c9b0f 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > @@ -310,6 +310,9 @@ struct intel_engine_cs {
> > u32 context_size;
> > u32 mmio_base;
> > + u32 lri_mmio_base;
> > + u32 lri_cmd_mode;
> > +
> > /*
> > * Some w/a require forcewake to be held (which prevents RC6) while
> > * a particular engine is active. If so, we set fw_domain to which
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gpu_commands.h b/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> > index 2694dbb9967e..f0f101134fd8 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> > @@ -134,8 +134,14 @@
> > * simply ignores the register load under certain conditions.
> > * - One can actually load arbitrary many arbitrary registers: Simply issue x
> > * address/value pairs. Don't overdue it, though, x <= 2^4 must hold!
> > + * - Newer hardware supports engine relative addressing but older hardware does
> > + * not. This is required for hw engine load balancing. The
> > + * MI_LOAD_REGISTER_IMM_REL macro can be used on both newer and older
> > + * hardware.
> > */
> > #define MI_LOAD_REGISTER_IMM(x) MI_INSTR(0x22, 2*(x)-1)
> > +#define MI_LOAD_REGISTER_IMM_REL(egine, x) \
> > + (MI_LOAD_REGISTER_IMM(x) | engine->lri_cmd_mode)
>
> This naming is a bit confusing, because MI_LOAD_REGISTER_IMM_REL is not
> actually always relative so we also need to be careful of how we provide the
> register values (i.e. with or without the mmio base). Also a bit worrying
> for future proofing, since we'd need to make sure that any new CS register
> access goes explicitly relative. Just my 2 cents, I know there was
> contention on this patch in the past so I'm not going to jump in on the
> fight :)
>
In the LRC the upper bits of the base is just ignored, while in ring it
is added. It is a bit confusing but the comment message explains this.
MI_LOAD_REGISTER_IMM_REL was Tvrtko's suggestion and I personally like
it. It is total bikeshed how this should look, I'd say let's go with
this and move on.
> I have not checked if any of the other numerous instances of
> MI_LOAD_REGISTER_IMM would benefit from going relative. I assume none is
> strictly required, since otherwise virtual engines wouldn't work.
>
I did a quick browse of the driver and I think I am missing some
instances. Let scrub the driver + fix this up with my next trybot
attempt.
Matt
> Daniele
>
> > /* Gen11+. addr = base + (ctx_restore ? offset & GENMASK(12,2) : offset) */
> > #define MI_LRI_LRM_CS_MMIO REG_BIT(19)
> > #define MI_LRI_FORCE_POSTED (1<<12)
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index aafe2a4df496..390628666564 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -44,11 +44,9 @@ static void set_offsets(u32 *regs,
> > flags = *data >> 6;
> > data++;
> > - *regs = MI_LOAD_REGISTER_IMM(count);
> > + *regs = MI_LOAD_REGISTER_IMM_REL(engine, count);
> > if (flags & POSTED)
> > *regs |= MI_LRI_FORCE_POSTED;
> > - if (INTEL_GEN(engine->i915) >= 11)
> > - *regs |= MI_LRI_LRM_CS_MMIO;
> > regs++;
> > GEM_BUG_ON(!count);
>
