>
> Currently the FE is spinning way too fast when polling for new work in
> the FE idleloop. As each poll fetches 16 bytes from memory, a GPU running
> at 1GHz with the current setting of 200 wait cycle between fetches causes
> 80 MB/s of memory traffic just to check for new work when the GPU is
> otherwise idle, which is more FE traffic than in some GPU loaded cases.
>
> Significantly increase the number of wait cycles to slow down the poll
> interval to ~30µs, limiting the FE idle memory traffic to 512 KB/s, while
> providing a max latency which should not hurt most use-cases. The FE WAIT
> command seems to have some unknown discrete steps in the wait cycles so
> we may over/undershoot the target a bit, but that should be harmless.
>
> If the GPU core base frequency is unknown keep the 200 wait cycles as
> a sane default.
>
> Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Reviewed-by: Christian Gmeiner <cgmeiner@xxxxxxxxxx>
> ---
> v2: Don't speed up when the GPU core frequency is unknown.
> ---
> drivers/gpu/drm/etnaviv/etnaviv_buffer.c | 11 ++++++-----
> drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 8 ++++++++
> drivers/gpu/drm/etnaviv/etnaviv_gpu.h | 1 +
> 3 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_buffer.c b/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
> index cf741c5c82d2..384df1659be6 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
> @@ -53,11 +53,12 @@ static inline void CMD_END(struct etnaviv_cmdbuf *buffer)
> OUT(buffer, VIV_FE_END_HEADER_OP_END);
> }
>
> -static inline void CMD_WAIT(struct etnaviv_cmdbuf *buffer)
> +static inline void CMD_WAIT(struct etnaviv_cmdbuf *buffer,
> + unsigned int waitcycles)
> {
> buffer->user_size = ALIGN(buffer->user_size, 8);
>
> - OUT(buffer, VIV_FE_WAIT_HEADER_OP_WAIT | 200);
> + OUT(buffer, VIV_FE_WAIT_HEADER_OP_WAIT | waitcycles);
> }
>
> static inline void CMD_LINK(struct etnaviv_cmdbuf *buffer,
> @@ -168,7 +169,7 @@ u16 etnaviv_buffer_init(struct etnaviv_gpu *gpu)
> /* initialize buffer */
> buffer->user_size = 0;
>
> - CMD_WAIT(buffer);
> + CMD_WAIT(buffer, gpu->fe_waitcycles);
> CMD_LINK(buffer, 2,
> etnaviv_cmdbuf_get_va(buffer, &gpu->mmu_context->cmdbuf_mapping)
> + buffer->user_size - 4);
> @@ -320,7 +321,7 @@ void etnaviv_sync_point_queue(struct etnaviv_gpu *gpu, unsigned int event)
> CMD_END(buffer);
>
> /* Append waitlink */
> - CMD_WAIT(buffer);
> + CMD_WAIT(buffer, gpu->fe_waitcycles);
> CMD_LINK(buffer, 2,
> etnaviv_cmdbuf_get_va(buffer, &gpu->mmu_context->cmdbuf_mapping)
> + buffer->user_size - 4);
> @@ -503,7 +504,7 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
>
> CMD_LOAD_STATE(buffer, VIVS_GL_EVENT, VIVS_GL_EVENT_EVENT_ID(event) |
> VIVS_GL_EVENT_FROM_PE);
> - CMD_WAIT(buffer);
> + CMD_WAIT(buffer, gpu->fe_waitcycles);
> CMD_LINK(buffer, 2,
> etnaviv_cmdbuf_get_va(buffer, &gpu->mmu_context->cmdbuf_mapping)
> + buffer->user_size - 4);
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> index de8c9894967c..63b929b1e5d1 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> @@ -493,6 +493,14 @@ static void etnaviv_gpu_update_clock(struct etnaviv_gpu *gpu)
> clock |= VIVS_HI_CLOCK_CONTROL_FSCALE_VAL(fscale);
> etnaviv_gpu_load_clock(gpu, clock);
> }
> +
> + /*
> + * Choose number of wait cycles to target a ~30us (1/32768) max latency
> + * until new work is picked up by the FE when it polls in the idle loop.
> + * If the GPU base frequency is unknown use 200 wait cycles.
> + */
> + gpu->fe_waitcycles = clamp(gpu->base_rate_core >> (15 - gpu->freq_scale),
> + 200UL, 0xffffUL);
> }
>
> static int etnaviv_hw_reset(struct etnaviv_gpu *gpu)
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
> index 98c6f9c320fc..e1e1de59c38d 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
> @@ -150,6 +150,7 @@ struct etnaviv_gpu {
> struct clk *clk_shader;
>
> unsigned int freq_scale;
> + unsigned int fe_waitcycles;
> unsigned long base_rate_core;
> unsigned long base_rate_shader;
> };
> --
> 2.39.2
>
--
greets
--
Christian Gmeiner, MSc
https://christian-gmeiner.info/privacypolicy
