Re: [PATCH v3 06/10] drm/msm/A6xx: Use posamble to reset counters on preemption

[Akhil P Oommen]

On Mon, Sep 09, 2024 at 05:07:42PM +0200, Antonino Maniscalco wrote:
> On 9/6/24 10:08 PM, Akhil P Oommen wrote:
> > On Thu, Sep 05, 2024 at 04:51:24PM +0200, Antonino Maniscalco wrote:
> > > Use the postamble to reset perf counters when switching between rings,
> > > except when sysprof is enabled, analogously to how they are reset
> > > between submissions when switching pagetables.
> > > 
> > > Signed-off-by: Antonino Maniscalco <antomani103@xxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/msm/adreno/a6xx_gpu.c     | 20 ++++++++++++++++++-
> > >   drivers/gpu/drm/msm/adreno/a6xx_gpu.h     |  5 +++++
> > >   drivers/gpu/drm/msm/adreno/a6xx_preempt.c | 32 +++++++++++++++++++++++++++++++
> > >   drivers/gpu/drm/msm/adreno/adreno_gpu.h   |  7 +++++--
> > >   4 files changed, 61 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > index ed0b138a2d66..710ec3ce2923 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > @@ -366,7 +366,8 @@ static void a6xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > >   static void a6xx_emit_set_pseudo_reg(struct msm_ringbuffer *ring,
> > >   		struct a6xx_gpu *a6xx_gpu, struct msm_gpu_submitqueue *queue)
> > >   {
> > > -	u64 preempt_offset_priv_secure;
> > > +	bool sysprof = refcount_read(&a6xx_gpu->base.base.sysprof_active) > 1;
> > > +	u64 preempt_offset_priv_secure, preempt_postamble;
> > >   	OUT_PKT7(ring, CP_SET_PSEUDO_REG, 15);
> > > @@ -398,6 +399,23 @@ static void a6xx_emit_set_pseudo_reg(struct msm_ringbuffer *ring,
> > >   	/* seems OK to set to 0 to disable it */
> > >   	OUT_RING(ring, 0);
> > >   	OUT_RING(ring, 0);
> > > +
> > > +	/* if not profiling set postamble to clear perfcounters, else clear it */
> > > +	if (!sysprof && a6xx_gpu->preempt_postamble_len) {

Setting len = 0 is enough to skip processing postamble packets. So how
about a simpler:

len = a6xx_gpu->preempt_postamble_len;
if (sysprof)
	len = 0;

OUT_PKT7(ring, CP_SET_AMBLE, 3);
OUT_RING(ring, lower_32_bits(preempt_postamble));
OUT_RING(ring, upper_32_bits(preempt_postamble));
OUT_RING(ring, CP_SET_AMBLE_2_DWORDS(len) |
		CP_SET_AMBLE_2_TYPE(KMD_AMBLE_TYPE));

> > > +		preempt_postamble = a6xx_gpu->preempt_postamble_iova;
> > > +
> > > +		OUT_PKT7(ring, CP_SET_AMBLE, 3);
> > > +		OUT_RING(ring, lower_32_bits(preempt_postamble));
> > > +		OUT_RING(ring, upper_32_bits(preempt_postamble));
> > > +		OUT_RING(ring, CP_SET_AMBLE_2_DWORDS(
> > > +					a6xx_gpu->preempt_postamble_len) |
> > > +				CP_SET_AMBLE_2_TYPE(KMD_AMBLE_TYPE));
> > > +	} else {
> > 
> > Why do we need this else part?
> 
> Wouldn't the postmable remain set if we don't explicitly set it to 0?

Aah, that is a genuine concern. I am not sure! Lets keep it.

> 
> > 
> > > +		OUT_PKT7(ring, CP_SET_AMBLE, 3);
> > > +		OUT_RING(ring, 0);
> > > +		OUT_RING(ring, 0);
> > > +		OUT_RING(ring, CP_SET_AMBLE_2_TYPE(KMD_AMBLE_TYPE));
> > > +	}
> > >   }
> > >   static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > > index da10060e38dc..b009732c08c5 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
> > > @@ -71,6 +71,11 @@ struct a6xx_gpu {
> > >   	bool uses_gmem;
> > >   	bool skip_save_restore;
> > > +	struct drm_gem_object *preempt_postamble_bo;
> > > +	void *preempt_postamble_ptr;
> > > +	uint64_t preempt_postamble_iova;
> > > +	uint64_t preempt_postamble_len;
> > > +
> > >   	struct a6xx_gmu gmu;
> > >   	struct drm_gem_object *shadow_bo;
> > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_preempt.c b/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > > index 1caff76aca6e..ec44f44d925f 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_preempt.c
> > > @@ -346,6 +346,28 @@ static int preempt_init_ring(struct a6xx_gpu *a6xx_gpu,
> > >   	return 0;
> > >   }
> > > +static void preempt_prepare_postamble(struct a6xx_gpu *a6xx_gpu)
> > > +{
> > > +	u32 *postamble = a6xx_gpu->preempt_postamble_ptr;
> > > +	u32 count = 0;
> > > +
> > > +	postamble[count++] = PKT7(CP_REG_RMW, 3);
> > > +	postamble[count++] = REG_A6XX_RBBM_PERFCTR_SRAM_INIT_CMD;
> > > +	postamble[count++] = 0;
> > > +	postamble[count++] = 1;
> > > +
> > > +	postamble[count++] = PKT7(CP_WAIT_REG_MEM, 6);
> > > +	postamble[count++] = CP_WAIT_REG_MEM_0_FUNCTION(WRITE_EQ);
> > > +	postamble[count++] = CP_WAIT_REG_MEM_1_POLL_ADDR_LO(
> > > +				REG_A6XX_RBBM_PERFCTR_SRAM_INIT_STATUS);
> > > +	postamble[count++] = CP_WAIT_REG_MEM_2_POLL_ADDR_HI(0);
> > > +	postamble[count++] = CP_WAIT_REG_MEM_3_REF(0x1);
> > > +	postamble[count++] = CP_WAIT_REG_MEM_4_MASK(0x1);
> > > +	postamble[count++] = CP_WAIT_REG_MEM_5_DELAY_LOOP_CYCLES(0);
> > 
> > Isn't it better to just replace this with NOP packets when sysprof is
> > enabled, just before triggering preemption? It will help to have an
> > immediate effect.
> > 
> > -Akhil
> > 
> 
> Mmm, this being a postamble I wonder whether we have the guarantee that it
> finishes execution before the IRQ is called so updating it doesn't race with
> the CP executing it.

Yes, it will be complete. But on a second thought now, this suggestion from me
looks like an overkill.

-Akhil.

> 
> > > +
> > > +	a6xx_gpu->preempt_postamble_len = count;
> > > +}
> > > +
> > >   void a6xx_preempt_fini(struct msm_gpu *gpu)
> > >   {
> > >   	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> > > @@ -376,6 +398,16 @@ void a6xx_preempt_init(struct msm_gpu *gpu)
> > >   	a6xx_gpu->uses_gmem = 1;
> > >   	a6xx_gpu->skip_save_restore = 1;
> > > +	a6xx_gpu->preempt_postamble_ptr  = msm_gem_kernel_new(gpu->dev,
> > > +			PAGE_SIZE, MSM_BO_WC | MSM_BO_MAP_PRIV,
> > > +			gpu->aspace, &a6xx_gpu->preempt_postamble_bo,
> > > +			&a6xx_gpu->preempt_postamble_iova);
> > > +
> > > +	preempt_prepare_postamble(a6xx_gpu);
> > > +
> > > +	if (IS_ERR(a6xx_gpu->preempt_postamble_ptr))
> > > +		goto fail;
> > > +
> > >   	timer_setup(&a6xx_gpu->preempt_timer, a6xx_preempt_timer, 0);
> > >   	return;
> > > diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.h b/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> > > index 6b1888280a83..87098567483b 100644
> > > --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> > > +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> > > @@ -610,12 +610,15 @@ OUT_PKT4(struct msm_ringbuffer *ring, uint16_t regindx, uint16_t cnt)
> > >   	OUT_RING(ring, PKT4(regindx, cnt));
> > >   }
> > > +#define PKT7(opcode, cnt) \
> > > +	(CP_TYPE7_PKT | (cnt << 0) | (PM4_PARITY(cnt) << 15) | \
> > > +		((opcode & 0x7F) << 16) | (PM4_PARITY(opcode) << 23))
> > > +
> > >   static inline void
> > >   OUT_PKT7(struct msm_ringbuffer *ring, uint8_t opcode, uint16_t cnt)
> > >   {
> > >   	adreno_wait_ring(ring, cnt + 1);
> > > -	OUT_RING(ring, CP_TYPE7_PKT | (cnt << 0) | (PM4_PARITY(cnt) << 15) |
> > > -		((opcode & 0x7F) << 16) | (PM4_PARITY(opcode) << 23));
> > > +	OUT_RING(ring, PKT7(opcode, cnt));
> > >   }
> > >   struct msm_gpu *a2xx_gpu_init(struct drm_device *dev);
> > > 
> > > -- 
> > > 2.46.0
> > > 
> 
> Best regards,
> -- 
> Antonino Maniscalco <antomani103@xxxxxxxxx>
>