[Mesa-dev] [PATCH 4/4] OPTIONAL: anv/gen9: Optimize slice and subslice load balancing behavior.
Jason Ekstrand
jason at jlekstrand.net
Sat Aug 10 21:43:20 UTC 2019
On Sat, Aug 10, 2019 at 2:22 PM Francisco Jerez <currojerez at riseup.net>
wrote:
> Jason Ekstrand <jason at jlekstrand.net> writes:
>
> > On Fri, Aug 9, 2019 at 7:22 PM Francisco Jerez <currojerez at riseup.net>
> > wrote:
> >
> >> See "i965/gen9: Optimize slice and subslice load balancing behavior."
> >> for the rationale. Marked optional because no performance evaluation
> >> has been done on this commit, it is provided to match the hashing
> >> settings of the Iris driver. Test reports welcome.
> >>
> >
> > Improves Aztec Ruins by 2.7% (tested 5 times in each configuration). I
> > also tested Batman: Arkham City but it only reports integer FPS numbers
> and
> > no change was noticable.
> >
> >
> >> ---
> >> src/intel/vulkan/anv_genX.h | 4 ++
> >> src/intel/vulkan/anv_private.h | 6 ++
> >> src/intel/vulkan/genX_blorp_exec.c | 6 ++
> >> src/intel/vulkan/genX_cmd_buffer.c | 96 ++++++++++++++++++++++++++++++
> >> 4 files changed, 112 insertions(+)
> >>
> >> diff --git a/src/intel/vulkan/anv_genX.h b/src/intel/vulkan/anv_genX.h
> >> index a5435e566a3..06c6b467acf 100644
> >> --- a/src/intel/vulkan/anv_genX.h
> >> +++ b/src/intel/vulkan/anv_genX.h
> >> @@ -44,6 +44,10 @@ void genX(cmd_buffer_apply_pipe_flushes)(struct
> >> anv_cmd_buffer *cmd_buffer);
> >>
> >> void genX(cmd_buffer_emit_gen7_depth_flush)(struct anv_cmd_buffer
> >> *cmd_buffer);
> >>
> >> +void genX(cmd_buffer_emit_hashing_mode)(struct anv_cmd_buffer
> *cmd_buffer,
> >> + unsigned width, unsigned
> height,
> >> + unsigned scale);
> >> +
> >> void genX(flush_pipeline_select_3d)(struct anv_cmd_buffer *cmd_buffer);
> >> void genX(flush_pipeline_select_gpgpu)(struct anv_cmd_buffer
> *cmd_buffer);
> >>
> >> diff --git a/src/intel/vulkan/anv_private.h
> >> b/src/intel/vulkan/anv_private.h
> >> index 2465f264354..b381386a716 100644
> >> --- a/src/intel/vulkan/anv_private.h
> >> +++ b/src/intel/vulkan/anv_private.h
> >> @@ -2421,6 +2421,12 @@ struct anv_cmd_state {
> >>
> >> bool
> >> conditional_render_enabled;
> >>
> >> + /**
> >> + * Last rendering scale argument provided to
> >> + * genX(cmd_buffer_emit_hashing_mode)().
> >> + */
> >> + unsigned current_hash_scale;
> >> +
> >> /**
> >> * Array length is anv_cmd_state::pass::attachment_count. Array
> >> content is
> >> * valid only when recording a render pass instance.
> >> diff --git a/src/intel/vulkan/genX_blorp_exec.c
> >> b/src/intel/vulkan/genX_blorp_exec.c
> >> index 1592e7f7e3d..e9eedc06696 100644
> >> --- a/src/intel/vulkan/genX_blorp_exec.c
> >> +++ b/src/intel/vulkan/genX_blorp_exec.c
> >> @@ -223,6 +223,12 @@ genX(blorp_exec)(struct blorp_batch *batch,
> >> genX(cmd_buffer_config_l3)(cmd_buffer, cfg);
> >> }
> >>
> >> + const unsigned scale = params->fast_clear_op ? UINT_MAX : 1;
> >> + if (cmd_buffer->state.current_hash_scale != scale) {
> >> + genX(cmd_buffer_emit_hashing_mode)(cmd_buffer, params->x1 -
> >> params->x0,
> >> + params->y1 - params->y0,
> scale);
> >> + }
> >> +
> >> #if GEN_GEN >= 11
> >> /* The PIPE_CONTROL command description says:
> >> *
> >> diff --git a/src/intel/vulkan/genX_cmd_buffer.c
> >> b/src/intel/vulkan/genX_cmd_buffer.c
> >> index 86ef1663ac4..e9e5570d49f 100644
> >> --- a/src/intel/vulkan/genX_cmd_buffer.c
> >> +++ b/src/intel/vulkan/genX_cmd_buffer.c
> >> @@ -1595,6 +1595,7 @@ genX(CmdExecuteCommands)(
> >> */
> >> primary->state.current_pipeline = UINT32_MAX;
> >> primary->state.current_l3_config = NULL;
> >> + primary->state.current_hash_scale = 0;
> >>
> >> /* Each of the secondary command buffers will use its own state base
> >> * address. We need to re-emit state base address for the primary
> >> after
> >> @@ -2663,6 +2664,9 @@ genX(cmd_buffer_flush_state)(struct anv_cmd_buffer
> >> *cmd_buffer)
> >>
> >> genX(cmd_buffer_config_l3)(cmd_buffer, pipeline->urb.l3_config);
> >>
> >> + if (cmd_buffer->state.current_hash_scale != 1)
> >> + genX(cmd_buffer_emit_hashing_mode)(cmd_buffer, UINT_MAX,
> UINT_MAX,
> >> 1);
> >>
> >
> > Can we do the check against current_hash_scale as an early return inside
> > the emit function since that's already where the "current" value is
> > updated? Maybe call it cmd_buffer_config_hashing_mode if "emit" no
> longer
> > seems right with that change? I don't really care about the rename.
> >
>
> That's what my first revision did. I moved the current_hash_scale check
> one level up because the function call overhead was visible in
> brw_upload_pipeline_state(), which is quite a hot path in i965.
That's a bit surprising but believable if the two are in different files
and there's a real function call going on there.
> That
> said I don't have any data justifying the change in the Vulkan driver --
> Because caller and callee are defined in the same compilation unit it
> *might* be that the function is inlined into
> genX(cmd_buffer_flush_state), though it's large enough that it may not
>
I highly doubt it would be a problem. It's a lot of lines of code but once
you optimize things a bit, it's actually quite a small function.
> be, either way it seemed like a good idea to do things consistently
> across drivers.
>
The functions right next to it for l3$ configuration and PIPELINE_SELECT
are both called unconditionally. IMO, consistency within the Vulkan driver
is more important than consistency between iris and ANV given that they
have completely different state tracking models.
--Jason
> >
> >> +
> >> genX(flush_pipeline_select_3d)(cmd_buffer);
> >>
> >> if (vb_emit) {
> >> @@ -3925,6 +3929,98 @@ genX(cmd_buffer_emit_gen7_depth_flush)(struct
> >> anv_cmd_buffer *cmd_buffer)
> >> }
> >> }
> >>
> >> +/**
> >> + * Update the pixel hashing modes that determine the balancing of PS
> >> threads
> >> + * across subslices and slices.
> >> + *
> >> + * \param width Width bound of the rendering area (already scaled down
> if
> >> \p
> >> + * scale is greater than 1).
> >> + * \param height Height bound of the rendering area (already scaled
> down
> >> if \p
> >> + * scale is greater than 1).
> >> + * \param scale The number of framebuffer samples that could
> potentially
> >> be
> >> + * affected by an individual channel of the PS thread.
> This
> >> is
> >> + * typically one for single-sampled rendering, but for
> >> operations
> >> + * like CCS resolves and fast clears a single PS
> invocation
> >> may
> >> + * update a huge number of pixels, in which case a finer
> >> + * balancing is desirable in order to maximally utilize
> the
> >> + * bandwidth available. UINT_MAX can be used as shorthand
> >> for
> >> + * "finest hashing mode available".
> >> + */
> >> +void
> >> +genX(cmd_buffer_emit_hashing_mode)(struct anv_cmd_buffer *cmd_buffer,
> >> + unsigned width, unsigned height,
> >> + unsigned scale)
> >> +{
> >> +#if GEN_GEN == 9
> >> + const struct gen_device_info *devinfo = &cmd_buffer->device->info;
> >> + const unsigned slice_hashing[] = {
> >> + /* Because all Gen9 platforms with more than one slice require
> >> + * three-way subslice hashing, a single "normal" 16x16 slice
> hashing
> >> + * block is guaranteed to suffer from substantial imbalance, with
> >> one
> >> + * subslice receiving twice as much work as the other two in the
> >> + * slice.
> >> + *
> >> + * The performance impact of that would be particularly severe
> when
> >> + * three-way hashing is also in use for slice balancing (which is
> >> the
> >> + * case for all Gen9 GT4 platforms), because one of the slices
> >> + * receives one every three 16x16 blocks in either direction,
> which
> >> + * is roughly the periodicity of the underlying subslice
> imbalance
> >> + * pattern ("roughly" because in reality the hardware's
> >> + * implementation of three-way hashing doesn't do exact modulo 3
> >> + * arithmetic, which somewhat decreases the magnitude of this
> effect
> >> + * in practice). This leads to a systematic subslice imbalance
> >> + * within that slice regardless of the size of the primitive.
> The
> >> + * 32x32 hashing mode guarantees that the subslice imbalance
> within
> >> a
> >> + * single slice hashing block is minimal, largely eliminating
> this
> >> + * effect.
> >> + */
> >> + _32x32,
> >> + /* Finest slice hashing mode available. */
> >> + NORMAL
> >> + };
> >> + const unsigned subslice_hashing[] = {
> >> + /* 16x16 would provide a slight cache locality benefit especially
> >> + * visible in the sampler L1 cache efficiency of low-bandwidth
> >> + * non-LLC platforms, but it comes at the cost of greater
> subslice
> >> + * imbalance for primitives of dimensions approximately
> intermediate
> >> + * between 16x4 and 16x16.
> >> + */
> >> + _16x4,
> >> + /* Finest subslice hashing mode available. */
> >> + _8x4
> >> + };
> >> + /* Dimensions of the smallest hashing block of a given hashing mode.
> >> If
> >> + * the rendering area is smaller than this there can't possibly be
> any
> >> + * benefit from switching to this mode, so we optimize out the
> >> + * transition.
> >> + */
> >> + const unsigned min_size[][2] = {
> >> + { 16, 4 },
> >> + { 8, 4 }
> >> + };
> >> + const unsigned idx = scale > 1;
> >> +
> >> + if (width > min_size[idx][0] || height > min_size[idx][1]) {
> >> + uint32_t gt_mode;
> >> +
> >> + anv_pack_struct(>_mode, GENX(GT_MODE),
> >> + .SliceHashing = (devinfo->num_slices > 1 ?
> >> slice_hashing[idx] : 0),
> >> + .SliceHashingMask = (devinfo->num_slices > 1 ?
> -1 :
> >> 0),
> >> + .SubsliceHashing = subslice_hashing[idx],
> >> + .SubsliceHashingMask = -1);
> >> +
> >> + anv_batch_emit(&cmd_buffer->batch, GENX(PIPE_CONTROL), pc) {
> >> + pc.StallAtPixelScoreboard = true;
> >> + pc.CommandStreamerStallEnable = true;
> >> + }
> >>
> >
> > This would be better as
> >
> > cmd_buffer->state.pending_pipe_bits |= ANV_PIPE_CS_STALL_BIT;
> > genX(cmd_buffer_apply_pipe_flushes)(cmd_buffer);
> >
> > That way workarounds get applied more properly and we can avoid redundant
> > PIPE_CONTROLs. apply_pipe_flushes will insert the StallAtPixelScoreboard
> > for you if needed. That said, maybe it's best to also OR in
> > ANV_PIPE_STALL_AT_SCOREBOARD_BIT just to be sure.
> >
>
> OK, changed locally.
>
> > Other than that, the patch looks good to me. Happy to see the perf
> bump. :)
> >
>
> Thanks for testing it out!
>
> > I did consider maybe trying to move things around so that the change is
> > done more as a subpass thing but there are some subtle interactions to
> > think through there and I'm convinced what you have here is correct so
> > let's go with it for now.
> >
> > --Jason
> >
> >
> >> +
> >> + emit_lri(&cmd_buffer->batch, GENX(GT_MODE_num), gt_mode);
> >> +
> >> + cmd_buffer->state.current_hash_scale = scale;
> >> + }
> >> +#endif
> >> +}
> >> +
> >> static void
> >> cmd_buffer_emit_depth_stencil(struct anv_cmd_buffer *cmd_buffer)
> >> {
> >> --
> >> 2.22.0
> >>
> >> _______________________________________________
> >> mesa-dev mailing list
> >> mesa-dev at lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
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