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

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Message-ID: <20210111153917.GA22594@xps13>
Date:   Mon, 11 Jan 2021 10:39:17 -0500
From:   Jeremy Cline <jcline@...hat.com>
To:     Christian König <christian.koenig@....com>
Cc:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        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

Hi,

On Mon, Jan 11, 2021 at 09:53:56AM +0100, Christian König wrote:
> 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.
> 

Thanks for the review. Is it acceptable to move the DC_FP_END()
annotation up to the last usage? Keeping it where it is is probably
do-able, but covers things like calls to resource_construct() which
makes use of struct resource_create_funcs. I'm guessing only a sub-set
of the implementations are called via this function, but having an
interface which can't sleep sometimes doesn't sound appealing.

Happy to do it, but before I go down that road I just wanted to make
sure that's what you had in mind.

Thanks,
Jeremy

> > ---
> >   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;
>