[PATCH] drm/amdgpu:guarantee 128dws between vm flush and IB(v3)
Christian König
deathsimple at vodafone.de
Fri Jan 20 08:48:17 UTC 2017
Yeah, thought about that possibility as well when we change the padding
to 256.
This happens every time our command submission uses more than 128 dw, in
this case you obviously have less than 128 padding.
But why doesn't this happen on Windows then?
Regards,
Christian.
Am 19.01.2017 um 15:49 schrieb Liu, Monk:
> And with more think on it, even the very first UMD cmd start with wptr at 256/512 position ( because ib test ends up at 255 aligned position), your approach still cannot satisfy 128 DW between SWTICH_BUFFER and Preamble IB (if no vm_flush) or 128 Nops before VM_flush (if needed) for the next frame.
>
> e.g. we insert 180 dw this frame, start from0, end up at 179, and ring_commit() padding NOPs and make wptr end up at 255, so only 75 NOPs is between SWITCH_BUFFER and next frame (assume we don't have vm-flush next frame)
>
> BR Monk
>
> -----Original Message-----
> From: Liu, Monk
> Sent: Thursday, January 19, 2017 10:39 PM
> To: 'Christian König' <deathsimple at vodafone.de>; amd-gfx at lists.freedesktop.org
> Subject: RE: [PATCH] drm/amdgpu:guarantee 128dws between vm flush and IB(v3)
>
> Christian
>
> I just found one issue in your previous patch ( the one you remove inserting 128nop before vm_fush and meanwhile set align_mask of GFX ring to 0xff)
>
> Because I checked amdgpu_ring_commit() again, this function will not guarantee current submit size aligned with 256 dw, instead it only guarantee the ring->wptr will be 256 dw aligned after amdgpu_ring_commit()
>
> So that means your approach can not make sure there will be 128 NOP before vm_flush at all !
>
> e.g. this frame start at 200 position of RB, and it submitted 50 dw so it ends at 249 position, you call amdgpu_ring_commit() now and it only padding 6 more NOPs to ring buffer, so wptr finnaly end at 255, that clearly not what we want originally ~ we want to insert 128 nop after SWITCH_BUFFER (or say, before vm_flush), but you only add 6 NOPs ....
>
> your approach only works with wptr == 0 for the first UMD submit
>
> BR Monk
>
> -----Original Message-----
> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On Behalf Of Christian K?nig
> Sent: Thursday, January 19, 2017 5:11 PM
> To: Liu, Monk <Monk.Liu at amd.com>; amd-gfx at lists.freedesktop.org
> Subject: Re: [PATCH] drm/amdgpu:guarantee 128dws between vm flush and IB(v3)
>
> Am 18.01.2017 um 12:42 schrieb Monk Liu:
>> previously we always insert 128nops behind vm_flush, which may lead to
>> DAMframe size above 256 dw and automatially aligned to 512 dw.
>>
>> now we calculate how many DWs already inserted after vm_flush and make
>> up for the reset to pad up to 128dws before emit_ib.
>> that way we only take 256 dw per submit.
>>
>> v2:
>> drop insert_nops in vm_flush
>> re-calculate the estimate frame size for gfx8 ring
>> v3:
>> calculate the gap between vm_flush and IB in cntx_cntl on an member
>> field of ring structure
>> v4:
>> set last_vm_flush_pos even for case of no vm flush.
>>
>> Change-Id: I0a1845de07c0b86ac1b77ac1a007e893144144fd
>> Signed-off-by: Monk Liu <Monk.Liu at amd.com>
>> ---
>> drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h | 1 +
>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 7 +++++++
>> drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c | 16 ++++++++++++----
>> 3 files changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
>> index c813cbe..332969f 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h
>> @@ -173,6 +173,7 @@ struct amdgpu_ring {
>> #if defined(CONFIG_DEBUG_FS)
>> struct dentry *ent;
>> #endif
>> + u32 last_vm_flush_pos;
>> };
>>
>> int amdgpu_ring_alloc(struct amdgpu_ring *ring, unsigned ndw); diff
>> --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> index d05546e..53fc5e0 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> @@ -396,6 +396,13 @@ int amdgpu_vm_flush(struct amdgpu_ring *ring, struct amdgpu_job *job)
>> amdgpu_vm_ring_has_compute_vm_bug(ring)))
>> amdgpu_ring_emit_pipeline_sync(ring);
>>
>> + /* when no vm-flush this frame, we still need to mark down
>> + * the position of the tail of hdp_flush, because we still
>> + * need to make sure there are 128 DWs between last SWITCH_BUFFER and
>> + * the emit_ib this frame. otherwise there is still VM fault occured on
>> + * constant engine.
>> + */
>> + ring->last_vm_flush_pos = ring->wptr;
>> if (ring->funcs->emit_vm_flush && (job->vm_needs_flush ||
>> amdgpu_vm_is_gpu_reset(adev, id))) {
>> struct fence *fence;
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
>> b/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
>> index 5f37313..dde4177 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c
>> @@ -6572,7 +6572,6 @@ static void gfx_v8_0_ring_emit_fence_gfx(struct amdgpu_ring *ring, u64 addr,
>> DATA_SEL(write64bit ? 2 : 1) | INT_SEL(int_sel ? 2 : 0));
>> amdgpu_ring_write(ring, lower_32_bits(seq));
>> amdgpu_ring_write(ring, upper_32_bits(seq));
>> -
>> }
>>
>> static void gfx_v8_0_ring_emit_pipeline_sync(struct amdgpu_ring
>> *ring) @@ -6636,9 +6635,8 @@ static void gfx_v8_0_ring_emit_vm_flush(struct amdgpu_ring *ring,
>> /* sync PFP to ME, otherwise we might get invalid PFP reads */
>> amdgpu_ring_write(ring, PACKET3(PACKET3_PFP_SYNC_ME, 0));
>> amdgpu_ring_write(ring, 0x0);
>> - /* GFX8 emits 128 dw nop to prevent CE access VM before vm_flush finish */
>> - amdgpu_ring_insert_nop(ring, 128);
>> }
>> + ring->last_vm_flush_pos = ring->wptr;
>> }
>>
>> static u32 gfx_v8_0_ring_get_wptr_compute(struct amdgpu_ring *ring)
>> @@ -6743,6 +6741,15 @@ static void gfx_v8_ring_emit_cntxcntl(struct amdgpu_ring *ring, uint32_t flags)
>> if (amdgpu_sriov_vf(ring->adev))
>> gfx_v8_0_ring_emit_de_meta_init(ring,
>> (flags & AMDGPU_VM_DOMAIN) ? AMDGPU_CSA_VADDR :
>> ring->adev->virt.csa_vmid0_addr);
>> +
>> + /* We need to pad some NOPs before emit_ib to prevent CE run ahead of
>> + * vm_flush, which may trigger VM fault. */
>> + if (ring->wptr > ring->last_vm_flush_pos) /* no wptr wrapping to RB head */
>> + amdgpu_ring_insert_nop(ring, 128 - (ring->wptr -
>> +ring->last_vm_flush_pos));
> This can easily result in a negative number, couldn't it?
>
>> + else
>> + if (ring->ptr_mask + 1 - ring->last_vm_flush_pos + ring->wptr < 128)
>> + amdgpu_ring_insert_nop(ring,
>> + 128 - (ring->ptr_mask + 1 - ring->last_vm_flush_pos +
>> +ring->wptr));
> I think it would be cleaner if you calculate the number of NOPs needed first for both cases and then check if the number isn't negative for both cases.
>
>> }
>>
>> static void gfx_v8_0_ring_emit_rreg(struct amdgpu_ring *ring,
>> uint32_t reg) @@ -7018,7 +7025,8 @@ static const struct amdgpu_ring_funcs gfx_v8_0_ring_funcs_gfx = {
>> 7 + /* gfx_v8_0_ring_emit_pipeline_sync */
>> 128 + 19 + /* gfx_v8_0_ring_emit_vm_flush */
>> 2 + /* gfx_v8_ring_emit_sb */
>> - 3 + 4 + 29, /* gfx_v8_ring_emit_cntxcntl including vgt flush/meta-data */
>> + 3 + 4 + 29 - /* gfx_v8_ring_emit_cntxcntl including vgt
>> +flush/meta-data */
> Please put the - on the next line. That is easy to miss and I asked myself for a moment why you want to add 20 here.
>
> Apart from that the patch looks good to me, Christian.
>
>> + 20 - 7 - 6 - 3 - 4 - 29, /* no need to count gds/hdp_flush/vm_flush
>> +fence/cntx_cntl/vgt_flush/meta-data anymore */
>> .emit_ib_size = 4, /* gfx_v8_0_ring_emit_ib_gfx */
>> .emit_ib = gfx_v8_0_ring_emit_ib_gfx,
>> .emit_fence = gfx_v8_0_ring_emit_fence_gfx,
>
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