Re: drm/etnaviv: slow down FE idle polling

[Sui Jingfeng <suijingfeng@xxxxxxxxxxx>]

Hi,

On 2023/6/15 17:04, Lucas Stach wrote:
> Am Donnerstag, dem 15.06.2023 um 12:09 +0800 schrieb Sui Jingfeng:
> > Hi,
> >
> > On 2023/6/7 20:59, Lucas Stach wrote:
> > > Currently the FE is spinning way too fast when polling for new work in
> > 'way' -> 'away'
> > > the FE idleloop.
> > 'idleloop' -> 'idle loop'
> > >    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
> > add a comma here.
> > >    so
> > > we may over/undershoot the target a bit, but that should be harmless.
> > overshoot or undershoot
> > > Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> > > Reviewed-by: Christian Gmeiner <cgmeiner@xxxxxxxxxx>
> > > ---
> > >    drivers/gpu/drm/etnaviv/etnaviv_buffer.c | 11 ++++++-----
> > >    drivers/gpu/drm/etnaviv/etnaviv_gpu.c    |  7 +++++++
> > >    drivers/gpu/drm/etnaviv/etnaviv_gpu.h    |  1 +
> > >    3 files changed, 14 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 41aab1aa330b..8c20dff32240 100644
> > > --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> > > @@ -493,6 +493,13 @@ 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.
> > > +	 */
> > > +	gpu->fe_waitcycles = min(gpu->base_rate_core >> (15 - gpu->freq_scale),
> > > +				 0xffffUL);
> > This patch is NOT effective on our hardware GC1000 v5037 (ls7a1000 +
> > ls3a5000).
> >
> > As the gpu->base_rate_core is 0,  so, in the end gpu->fe_waitcycles is
> > also zero.
> Uh, that's a problem, as the patch will then have the opposite effect
> on your platform by speeding up the idle loop. Thanks for catching
> this! I'll improve the patch to keep a reasonable amount of wait cycles
> in this case.

It's OK, no big problem as far as I can see. (it my platform's problem, 
not your problem)

Merge it is also OK, if we found something wrong we could fix it with a 
another patch.

> Regards,
> Lucas
>
> > But after apply this path, the glmark2 still run happily, no influence. So
> >
> >
> > Tested-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> >
> > >    }
> > >    
> > >    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;
> > >    };

--
Jingfeng