linux-kernel - Re: [PATCH] amdgpu: Avoid sleeping during FPU critical sections

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Date:   Mon, 11 Jan 2021 09:53:56 +0100
From:   Christian König <christian.koenig@....com>
To:     Jeremy Cline <jcline@...hat.com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Timothy Pearson <tpearson@...torengineering.com>
Subject: Re: [PATCH] amdgpu: Avoid sleeping during FPU critical sections

Am 08.01.21 um 22:58 schrieb Jeremy Cline:
> dcn20_resource_construct() includes a number of kzalloc(GFP_KERNEL)
> calls which can sleep, but kernel_fpu_begin() disables preemption and
> sleeping in this context is invalid.
>
> The only places the FPU appears to be required is in the
> init_soc_bounding_box() function and when calculating the
> {min,max}_fill_clk_mhz. Narrow the scope to just these two parts to
> avoid sleeping while using the FPU.
>
> Fixes: 7a8a3430be15 ("amdgpu: Wrap FPU dependent functions in dc20")
> Cc: Timothy Pearson <tpearson@...torengineering.com>
> Signed-off-by: Jeremy Cline <jcline@...hat.com>

Good catch, but I would rather replace the kzalloc(GFP_KERNEL) with a 
kzalloc(GFP_ATOMIC) for now.

We have tons of problems with this DC_FP_START()/DC_FP_END() annotations 
and are even in the process of moving them out of the file because the 
compiles tend to clutter FP registers even outside of the annotated 
ranges on some architectures.

Regards,
Christian.

> ---
>   drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
> index e04ecf0fc0db..a4fa5bf016c1 100644
> --- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
> +++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
> @@ -3622,6 +3622,7 @@ static bool init_soc_bounding_box(struct dc *dc,
>   	if (bb && ASICREV_IS_NAVI12_P(dc->ctx->asic_id.hw_internal_rev)) {
>   		int i;
>   
> +		DC_FP_START();
>   		dcn2_0_nv12_soc.sr_exit_time_us =
>   				fixed16_to_double_to_cpu(bb->sr_exit_time_us);
>   		dcn2_0_nv12_soc.sr_enter_plus_exit_time_us =
> @@ -3721,6 +3722,7 @@ static bool init_soc_bounding_box(struct dc *dc,
>   			dcn2_0_nv12_soc.clock_limits[i].dram_speed_mts =
>   					fixed16_to_double_to_cpu(bb->clock_limits[i].dram_speed_mts);
>   		}
> +		DC_FP_END();
>   	}
>   
>   	if (pool->base.pp_smu) {
> @@ -3777,8 +3779,6 @@ static bool dcn20_resource_construct(
>   	enum dml_project dml_project_version =
>   			get_dml_project_version(ctx->asic_id.hw_internal_rev);
>   
> -	DC_FP_START();
> -
>   	ctx->dc_bios->regs = &bios_regs;
>   	pool->base.funcs = &dcn20_res_pool_funcs;
>   
> @@ -3959,8 +3959,10 @@ static bool dcn20_resource_construct(
>   				ranges.reader_wm_sets[i].wm_inst = i;
>   				ranges.reader_wm_sets[i].min_drain_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MIN;
>   				ranges.reader_wm_sets[i].max_drain_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MAX;
> +				DC_FP_START();
>   				ranges.reader_wm_sets[i].min_fill_clk_mhz = (i > 0) ? (loaded_bb->clock_limits[i - 1].dram_speed_mts / 16) + 1 : 0;
>   				ranges.reader_wm_sets[i].max_fill_clk_mhz = loaded_bb->clock_limits[i].dram_speed_mts / 16;
> +				DC_FP_END();
>   
>   				ranges.num_reader_wm_sets = i + 1;
>   			}
> @@ -4125,12 +4127,10 @@ static bool dcn20_resource_construct(
>   		pool->base.oem_device = NULL;
>   	}
>   
> -	DC_FP_END();
>   	return true;
>   
>   create_fail:
>   
> -	DC_FP_END();
>   	dcn20_resource_destruct(pool);
>   
>   	return false;