Re: [PATCH] drm/amdgpu: refine kiq read register

[Christian König <christian.koenig@xxxxxxx>]

Hi Monk,

> Can we first get the first problem done ?

Please absolutely not! See the problem introduced here is quite worse 
than the actual fix.

Previously we ended up with an invalid value in a concurrent register 
read, now the KIQs overwrites its own commands and most likely causes a 
hang or the hardware to execute something random.

Instead of this crude hack please let us just allocate a fixed number of 
write back slots and use them round robin. Then we can make sure that we 
don't have more than a fixed number of reads in flight at the same time 
as well using the fence values.

This should fix both problems at the same time and not introduce another 
potential problematic hack.

If this patch is already committed please revert it immediately.

Regards,
Christian.

Am 20.04.20 um 08:20 schrieb Liu, Monk:
> Christian
>
> > > > Well I was under the assumption that this is actually what is done here.
> If that is not the case the patch is a rather clear NAK.
> <<<
>
> There are two kinds of problems in the current KIQ reading reg, Yintian tend to fix one of them but not all ...
>
> The first problem is :
> During the sleep of the first KIQ reading, another KIQ reading initiated an the read back register value flushed the first readback value, thus the first reading will get the wrong result.
> This is the issue yintian's patch to address, by put the readback value not in a shared WB but in a chunk DW of command submit
>
> The second problem is:
> Since we don't utilize GPU scheduler for KIQ submit thus if the KIQ is busy with some commands then those unfinished commands maybe overwritten by a new command submit, and that's not the
> Problem yintian's patch tend to address. Felex pointed it out which is fine and we can use another patch to address it, I'm also planning and scoping it.
>
> The optional way is:
> 1) We use GPU scheduler to manage KIQ activity, and all jobs are submitted  to KIQ through a IB, thus no overwritten will happen
> 2) we still skip gpu scheduler but always use IB to put jobs on KIQ, thus each JOB will occupy the fixed space/DW of RB, so we can avoid overwrite unfinished command
>
> We can discuss the second problem later
>
> Can we first get the first problem done ? thanks
>
>
> _____________________________________
> Monk Liu|GPU Virtualization Team |AMD
>
>
> -----Original Message-----
> From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>
> Sent: Monday, April 20, 2020 1:03 AM
> To: Kuehling, Felix <Felix.Kuehling@xxxxxxx>; Tao, Yintian <Yintian.Tao@xxxxxxx>; Liu, Monk <Monk.Liu@xxxxxxx>
> Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH] drm/amdgpu: refine kiq read register
>
> Am 17.04.20 um 17:39 schrieb Felix Kuehling:
> > Am 2020-04-17 um 2:53 a.m. schrieb Yintian Tao:
> > > According to the current kiq read register method, there will be race
> > > condition when using KIQ to read register if multiple clients want to
> > > read at same time just like the expample below:
> > > 1. client-A start to read REG-0 throguh KIQ 2. client-A poll the
> > > seqno-0 3. client-B start to read REG-1 through KIQ 4. client-B poll
> > > the seqno-1 5. the kiq complete these two read operation 6. client-A
> > > to read the register at the wb buffer and
> > >      get REG-1 value
> > >
> > > Therefore, directly make kiq write the register value at the ring
> > > buffer then there will be no race condition for the wb buffer.
> > >
> > > v2: supply the read_clock and move the reg_val_offs back
> > >
> > > Signed-off-by: Yintian Tao <yttao@xxxxxxx>
> > > ---
> > >    drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c  | 11 ++++------
> > >    drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h  |  1 -
> > >    drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h |  5 +++--
> > >    drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c   | 14 +++++-------
> > >    drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c    | 14 +++++-------
> > >    drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c    | 28 ++++++++++++------------
> > >    6 files changed, 33 insertions(+), 40 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > > index ea576b4260a4..4e1c0239e561 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > > @@ -304,10 +304,6 @@ int amdgpu_gfx_kiq_init_ring(struct
> > > amdgpu_device *adev,
> > >    
> > >    	spin_lock_init(&kiq->ring_lock);
> > >    
> > > -	r = amdgpu_device_wb_get(adev, &kiq->reg_val_offs);
> > > -	if (r)
> > > -		return r;
> > > -
> > >    	ring->adev = NULL;
> > >    	ring->ring_obj = NULL;
> > >    	ring->use_doorbell = true;
> > > @@ -331,7 +327,6 @@ int amdgpu_gfx_kiq_init_ring(struct amdgpu_device
> > > *adev,
> > >    
> > >    void amdgpu_gfx_kiq_free_ring(struct amdgpu_ring *ring)
> > >    {
> > > -	amdgpu_device_wb_free(ring->adev, ring->adev->gfx.kiq.reg_val_offs);
> > >    	amdgpu_ring_fini(ring);
> > >    }
> > >    
> > > @@ -675,12 +670,14 @@ uint32_t amdgpu_kiq_rreg(struct amdgpu_device *adev, uint32_t reg)
> > >    	uint32_t seq;
> > >    	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
> > >    	struct amdgpu_ring *ring = &kiq->ring;
> > > +	uint64_t reg_val_offs = 0;
> > >    
> > >    	BUG_ON(!ring->funcs->emit_rreg);
> > >    
> > >    	spin_lock_irqsave(&kiq->ring_lock, flags);
> > >    	amdgpu_ring_alloc(ring, 32);
> > > -	amdgpu_ring_emit_rreg(ring, reg);
> > > +	reg_val_offs = (ring->wptr & ring->buf_mask) + 30;
> > I think that should be (ring->wptr + 30) & ring->buf_mask. Otherwise
> > the reg_val_offset can be past the end of the ring.
> >
> > But that still leaves a problem if another command is submitted to the
> > KIQ before you read the returned reg_val from the ring. Your reg_val
> > can be overwritten by the new command and you get the wrong result. Or
> > the command can be overwritten with the reg_val, which will most
> > likely hang the CP.
> >
> > You could allocate space on the KIQ ring with a NOP command to prevent
> > that space from being overwritten by other commands.
> Well I was under the assumption that this is actually what is done here.
> If that is not the case the patch is a rather clear NAK.
>
> Regards,
> Christian.
>
> > Regards,
> >     Felix
> >
> >
> > > +	amdgpu_ring_emit_rreg(ring, reg, reg_val_offs);
> > >    	amdgpu_fence_emit_polling(ring, &seq);
> > >    	amdgpu_ring_commit(ring);
> > >    	spin_unlock_irqrestore(&kiq->ring_lock, flags); @@ -707,7 +704,7
> > > @@ uint32_t amdgpu_kiq_rreg(struct amdgpu_device *adev, uint32_t reg)
> > >    	if (cnt > MAX_KIQ_REG_TRY)
> > >    		goto failed_kiq_read;
> > >    
> > > -	return adev->wb.wb[kiq->reg_val_offs];
> > > +	return ring->ring[reg_val_offs];
> > >    
> > >    failed_kiq_read:
> > >    	pr_err("failed to read reg:%x\n", reg); diff --git
> > > a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> > > index 634746829024..ee698f0246d8 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> > > @@ -103,7 +103,6 @@ struct amdgpu_kiq {
> > >    	struct amdgpu_ring	ring;
> > >    	struct amdgpu_irq_src	irq;
> > >    	const struct kiq_pm4_funcs *pmf;
> > > -	uint32_t			reg_val_offs;
> > >    };
> > >    
> > >    /*
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
> > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
> > > index f61664ee4940..a3d88f2aa9f4 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
> > > @@ -181,7 +181,8 @@ struct amdgpu_ring_funcs {
> > >    	void (*end_use)(struct amdgpu_ring *ring);
> > >    	void (*emit_switch_buffer) (struct amdgpu_ring *ring);
> > >    	void (*emit_cntxcntl) (struct amdgpu_ring *ring, uint32_t flags);
> > > -	void (*emit_rreg)(struct amdgpu_ring *ring, uint32_t reg);
> > > +	void (*emit_rreg)(struct amdgpu_ring *ring, uint32_t reg,
> > > +			  uint64_t reg_val_offs);
> > >    	void (*emit_wreg)(struct amdgpu_ring *ring, uint32_t reg, uint32_t val);
> > >    	void (*emit_reg_wait)(struct amdgpu_ring *ring, uint32_t reg,
> > >    			      uint32_t val, uint32_t mask); @@ -265,7 +266,7 @@ struct
> > > amdgpu_ring {
> > >    #define amdgpu_ring_emit_hdp_flush(r) (r)->funcs->emit_hdp_flush((r))
> > >    #define amdgpu_ring_emit_switch_buffer(r) (r)->funcs->emit_switch_buffer((r))
> > >    #define amdgpu_ring_emit_cntxcntl(r, d)
> > > (r)->funcs->emit_cntxcntl((r), (d)) -#define amdgpu_ring_emit_rreg(r,
> > > d) (r)->funcs->emit_rreg((r), (d))
> > > +#define amdgpu_ring_emit_rreg(r, d, o) (r)->funcs->emit_rreg((r),
> > > +(d), (o))
> > >    #define amdgpu_ring_emit_wreg(r, d, v) (r)->funcs->emit_wreg((r), (d), (v))
> > >    #define amdgpu_ring_emit_reg_wait(r, d, v, m) (r)->funcs->emit_reg_wait((r), (d), (v), (m))
> > >    #define amdgpu_ring_emit_reg_write_reg_wait(r, d0, d1, v, m)
> > > (r)->funcs->emit_reg_write_reg_wait((r), (d0), (d1), (v), (m)) diff
> > > --git a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
> > > b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
> > > index 0a03e2ad5d95..7c9a5e440509 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
> > > @@ -7594,21 +7594,19 @@ static void gfx_v10_0_ring_emit_frame_cntl(struct amdgpu_ring *ring, bool start,
> > >    	amdgpu_ring_write(ring, v | FRAME_CMD(start ? 0 : 1));
> > >    }
> > >    
> > > -static void gfx_v10_0_ring_emit_rreg(struct amdgpu_ring *ring,
> > > uint32_t reg)
> > > +static void gfx_v10_0_ring_emit_rreg(struct amdgpu_ring *ring, uint32_t reg,
> > > +				     uint64_t reg_val_offs)
> > >    {
> > > -	struct amdgpu_device *adev = ring->adev;
> > > -	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
> > > -
> > >    	amdgpu_ring_write(ring, PACKET3(PACKET3_COPY_DATA, 4));
> > >    	amdgpu_ring_write(ring, 0 |	/* src: register*/
> > >    				(5 << 8) |	/* dst: memory */
> > >    				(1 << 20));	/* write confirm */
> > >    	amdgpu_ring_write(ring, reg);
> > >    	amdgpu_ring_write(ring, 0);
> > > -	amdgpu_ring_write(ring, lower_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > -	amdgpu_ring_write(ring, upper_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, lower_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, upper_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > >    }
> > >    
> > >    static void gfx_v10_0_ring_emit_wreg(struct amdgpu_ring *ring,
> > > uint32_t reg, diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
> > > b/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
> > > index fc6c2f2bc76c..8e7eee7838e0 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
> > > @@ -6383,21 +6383,19 @@ static void gfx_v8_0_ring_emit_patch_cond_exec(struct amdgpu_ring *ring, unsigne
> > >    		ring->ring[offset] = (ring->ring_size >> 2) - offset + cur;
> > >    }
> > >    
> > > -static void gfx_v8_0_ring_emit_rreg(struct amdgpu_ring *ring,
> > > uint32_t reg)
> > > +static void gfx_v8_0_ring_emit_rreg(struct amdgpu_ring *ring, uint32_t reg,
> > > +				    uint64_t reg_val_offs)
> > >    {
> > > -	struct amdgpu_device *adev = ring->adev;
> > > -	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
> > > -
> > >    	amdgpu_ring_write(ring, PACKET3(PACKET3_COPY_DATA, 4));
> > >    	amdgpu_ring_write(ring, 0 |	/* src: register*/
> > >    				(5 << 8) |	/* dst: memory */
> > >    				(1 << 20));	/* write confirm */
> > >    	amdgpu_ring_write(ring, reg);
> > >    	amdgpu_ring_write(ring, 0);
> > > -	amdgpu_ring_write(ring, lower_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > -	amdgpu_ring_write(ring, upper_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, lower_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, upper_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > >    }
> > >    
> > >    static void gfx_v8_0_ring_emit_wreg(struct amdgpu_ring *ring,
> > > uint32_t reg, diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> > > b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> > > index 84fcf842316d..ff279b1f5c24 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> > > @@ -4046,11 +4046,13 @@ static uint64_t gfx_v9_0_kiq_read_clock(struct amdgpu_device *adev)
> > >    	uint32_t seq;
> > >    	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
> > >    	struct amdgpu_ring *ring = &kiq->ring;
> > > +	uint64_t reg_val_offs = 0;
> > >    
> > >    	BUG_ON(!ring->funcs->emit_rreg);
> > >    
> > >    	spin_lock_irqsave(&kiq->ring_lock, flags);
> > >    	amdgpu_ring_alloc(ring, 32);
> > > +	reg_val_offs = (ring->wptr & ring->buf_mask) + 30;
> > >    	amdgpu_ring_write(ring, PACKET3(PACKET3_COPY_DATA, 4));
> > >    	amdgpu_ring_write(ring, 9 |	/* src: register*/
> > >    				(5 << 8) |	/* dst: memory */
> > > @@ -4058,10 +4060,10 @@ static uint64_t gfx_v9_0_kiq_read_clock(struct amdgpu_device *adev)
> > >    				(1 << 20));	/* write confirm */
> > >    	amdgpu_ring_write(ring, 0);
> > >    	amdgpu_ring_write(ring, 0);
> > > -	amdgpu_ring_write(ring, lower_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > -	amdgpu_ring_write(ring, upper_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, lower_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, upper_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > >    	amdgpu_fence_emit_polling(ring, &seq);
> > >    	amdgpu_ring_commit(ring);
> > >    	spin_unlock_irqrestore(&kiq->ring_lock, flags); @@ -4088,8 +4090,8
> > > @@ static uint64_t gfx_v9_0_kiq_read_clock(struct amdgpu_device *adev)
> > >    	if (cnt > MAX_KIQ_REG_TRY)
> > >    		goto failed_kiq_read;
> > >    
> > > -	return (uint64_t)adev->wb.wb[kiq->reg_val_offs] |
> > > -		(uint64_t)adev->wb.wb[kiq->reg_val_offs + 1 ] << 32ULL;
> > > +	return (uint64_t)ring->ring[reg_val_offs] |
> > > +		(uint64_t)ring->ring[reg_val_offs + 1 ] << 32ULL;
> > >    
> > >    failed_kiq_read:
> > >    	pr_err("failed to read gpu clock\n"); @@ -5482,21 +5484,19 @@
> > > static void gfx_v9_0_ring_emit_patch_cond_exec(struct amdgpu_ring *ring, unsigne
> > >    		ring->ring[offset] = (ring->ring_size>>2) - offset + cur;
> > >    }
> > >    
> > > -static void gfx_v9_0_ring_emit_rreg(struct amdgpu_ring *ring,
> > > uint32_t reg)
> > > +static void gfx_v9_0_ring_emit_rreg(struct amdgpu_ring *ring, uint32_t reg,
> > > +				    uint64_t reg_val_offs)
> > >    {
> > > -	struct amdgpu_device *adev = ring->adev;
> > > -	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
> > > -
> > >    	amdgpu_ring_write(ring, PACKET3(PACKET3_COPY_DATA, 4));
> > >    	amdgpu_ring_write(ring, 0 |	/* src: register*/
> > >    				(5 << 8) |	/* dst: memory */
> > >    				(1 << 20));	/* write confirm */
> > >    	amdgpu_ring_write(ring, reg);
> > >    	amdgpu_ring_write(ring, 0);
> > > -	amdgpu_ring_write(ring, lower_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > -	amdgpu_ring_write(ring, upper_32_bits(adev->wb.gpu_addr +
> > > -				kiq->reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, lower_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > > +	amdgpu_ring_write(ring, upper_32_bits(ring->gpu_addr +
> > > +					      reg_val_offs * 4));
> > >    }
> > >    
> > >    static void gfx_v9_0_ring_emit_wreg(struct amdgpu_ring *ring,
> > > uint32_t reg,
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