Re: [Intel-gfx] [PATCH] drm/i915: avoid concurrent writes to aux_inv

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 28/03/2022 04:16, fei.yang@intel.com wrote:
> From: Fei Yang <fei.yang@intel.com>
> 
> GPU hangs have been observed when multiple engines write to the
> same aux_inv register at the same time. To avoid this each engine
> should only invalidate its own auxiliary table. The function
> gen12_emit_flush_xcs() currently invalidate the auxiliary table for
> all engines because the rq->engine is not necessarily the engine
> eventually carrying out the request, and potentially the engine
> could even be a virtual one (with engine->instance being -1).
> With the MMIO remap feature, we can actually set bit 17 of MI_LRI
> instruction and let the hardware to figure out the local aux_inv
> register at runtime to avoid invalidating auxiliary table for all
> engines.
> 
> Bspec: 45728
> 
> v2: Invalidate AUX table for indirect context as well.
> 
> Cc: Stuart Summers <stuart.summers@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Signed-off-by: Chris Wilson <chris.p.wilson@intel.com>
> Signed-off-by: Fei Yang <fei.yang@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/gen8_engine_cs.c     | 48 ++++----------------
>   drivers/gpu/drm/i915/gt/gen8_engine_cs.h     |  4 +-
>   drivers/gpu/drm/i915/gt/intel_gpu_commands.h |  1 +
>   drivers/gpu/drm/i915/gt/intel_lrc.c          | 12 +++++
>   4 files changed, 26 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> index 36148887c699..8178be083b42 100644
> --- a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> @@ -6,7 +6,6 @@
>   #include "gen8_engine_cs.h"
>   #include "i915_drv.h"
>   #include "intel_gpu_commands.h"
> -#include "intel_gt_regs.h"
>   #include "intel_lrc.h"
>   #include "intel_ring.h"
>   
> @@ -165,33 +164,9 @@ static u32 preparser_disable(bool state)
>   	return MI_ARB_CHECK | 1 << 8 | state;
>   }
>   
> -static i915_reg_t aux_inv_reg(const struct intel_engine_cs *engine)
> +u32 *gen12_emit_aux_table_inv(const i915_reg_t inv_reg, u32 *cs)

I think all helpers which emit to ring take cs as the first argument so 
it would be good to make this consistent.

>   {
> -	static const i915_reg_t vd[] = {
> -		GEN12_VD0_AUX_NV,
> -		GEN12_VD1_AUX_NV,
> -		GEN12_VD2_AUX_NV,
> -		GEN12_VD3_AUX_NV,
> -	};
> -
> -	static const i915_reg_t ve[] = {
> -		GEN12_VE0_AUX_NV,
> -		GEN12_VE1_AUX_NV,
> -	};
> -
> -	if (engine->class == VIDEO_DECODE_CLASS)
> -		return vd[engine->instance];
> -
> -	if (engine->class == VIDEO_ENHANCEMENT_CLASS)
> -		return ve[engine->instance];
> -
> -	GEM_BUG_ON("unknown aux_inv reg\n");
> -	return INVALID_MMIO_REG;
> -}
> -
> -static u32 *gen12_emit_aux_table_inv(const i915_reg_t inv_reg, u32 *cs)
> -{
> -	*cs++ = MI_LOAD_REGISTER_IMM(1);
> +	*cs++ = MI_LOAD_REGISTER_IMM(1) | MI_LRI_MMIO_REMAP_EN;
>   	*cs++ = i915_mmio_reg_offset(inv_reg);
>   	*cs++ = AUX_INV;
>   	*cs++ = MI_NOOP;
> @@ -293,10 +268,12 @@ int gen12_emit_flush_xcs(struct i915_request *rq, u32 mode)
>   	if (mode & EMIT_INVALIDATE) {
>   		cmd += 2;
>   
> -		if (!HAS_FLAT_CCS(rq->engine->i915)) {
> +		if (!HAS_FLAT_CCS(rq->engine->i915) &&
> +		    (rq->engine->class == VIDEO_DECODE_CLASS ||
> +		     rq->engine->class == VIDEO_ENHANCEMENT_CLASS)) {
>   			aux_inv = rq->engine->mask & ~BIT(BCS0);
>   			if (aux_inv)
> -				cmd += 2 * hweight32(aux_inv) + 2;
> +				cmd += 4;
>   		}
>   	}
>   
> @@ -329,15 +306,10 @@ int gen12_emit_flush_xcs(struct i915_request *rq, u32 mode)
>   	*cs++ = 0; /* value */
>   
>   	if (aux_inv) { /* hsdes: 1809175790 */
> -		struct intel_engine_cs *engine;
> -		unsigned int tmp;
> -
> -		*cs++ = MI_LOAD_REGISTER_IMM(hweight32(aux_inv));
> -		for_each_engine_masked(engine, rq->engine->gt, aux_inv, tmp) {
> -			*cs++ = i915_mmio_reg_offset(aux_inv_reg(engine));
> -			*cs++ = AUX_INV;
> -		}
> -		*cs++ = MI_NOOP;
> +		if (rq->engine->class == VIDEO_DECODE_CLASS)
> +			cs = gen12_emit_aux_table_inv(GEN12_VD0_AUX_NV, cs);
> +		else
> +			cs = gen12_emit_aux_table_inv(GEN12_VE0_AUX_NV, cs);

Not sure if, here and below, it would be worth to put register in a 
local and then have a single function call - up to you.

>   	}
>   
>   	if (mode & EMIT_INVALIDATE)
> diff --git a/drivers/gpu/drm/i915/gt/gen8_engine_cs.h b/drivers/gpu/drm/i915/gt/gen8_engine_cs.h
> index cc6e21d3662a..94f589e73d10 100644
> --- a/drivers/gpu/drm/i915/gt/gen8_engine_cs.h
> +++ b/drivers/gpu/drm/i915/gt/gen8_engine_cs.h
> @@ -10,7 +10,7 @@
>   #include <linux/types.h>
>   
>   #include "i915_gem.h" /* GEM_BUG_ON */
> -
> +#include "intel_gt_regs.h"
>   #include "intel_gpu_commands.h"
>   
>   struct i915_request;
> @@ -38,6 +38,8 @@ u32 *gen8_emit_fini_breadcrumb_rcs(struct i915_request *rq, u32 *cs);
>   u32 *gen11_emit_fini_breadcrumb_rcs(struct i915_request *rq, u32 *cs);
>   u32 *gen12_emit_fini_breadcrumb_rcs(struct i915_request *rq, u32 *cs);
>   
> +u32 *gen12_emit_aux_table_inv(const i915_reg_t inv_reg, u32 *cs);
> +
>   static inline u32 *
>   __gen8_emit_pipe_control(u32 *batch, u32 flags0, u32 flags1, u32 offset)
>   {
> diff --git a/drivers/gpu/drm/i915/gt/intel_gpu_commands.h b/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> index d112ffd56418..4243be030bc1 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gpu_commands.h
> @@ -144,6 +144,7 @@
>   #define MI_LOAD_REGISTER_IMM(x)	MI_INSTR(0x22, 2*(x)-1)
>   /* Gen11+. addr = base + (ctx_restore ? offset & GENMASK(12,2) : offset) */
>   #define   MI_LRI_LRM_CS_MMIO		REG_BIT(19)
> +#define   MI_LRI_MMIO_REMAP_EN		REG_BIT(17)
>   #define   MI_LRI_FORCE_POSTED		(1<<12)
>   #define MI_LOAD_REGISTER_IMM_MAX_REGS (126)
>   #define MI_STORE_REGISTER_MEM        MI_INSTR(0x24, 1)
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 07bef7128fdb..7581ef9e2cce 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1208,6 +1208,10 @@ gen12_emit_indirect_ctx_rcs(const struct intel_context *ce, u32 *cs)
>   	    IS_DG2_G11(ce->engine->i915))
>   		cs = gen8_emit_pipe_control(cs, PIPE_CONTROL_INSTRUCTION_CACHE_INVALIDATE, 0);
>   
> +	/* hsdes: 1809175790 */
> +	if (!HAS_FLAT_CCS(ce->engine->i915))
> +		cs = gen12_emit_aux_table_inv(GEN12_GFX_CCS_AUX_NV, cs);
> +
>   	return cs;
>   }
>   
> @@ -1225,6 +1229,14 @@ gen12_emit_indirect_ctx_xcs(const struct intel_context *ce, u32 *cs)
>   						    PIPE_CONTROL_INSTRUCTION_CACHE_INVALIDATE,
>   						    0);
>   
> +	/* hsdes: 1809175790 */
> +	if (!HAS_FLAT_CCS(ce->engine->i915)) {
> +		if (ce->engine->class == VIDEO_DECODE_CLASS)
> +			cs = gen12_emit_aux_table_inv(GEN12_VD0_AUX_NV, cs);
> +		else if (ce->engine->class == VIDEO_ENHANCEMENT_CLASS)
> +			cs = gen12_emit_aux_table_inv(GEN12_VE0_AUX_NV, cs);
> +	}
> +
>   	return cs;
>   }
>   

Apart from the cs re-order looks good to me.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko