[PATCH v3 2/2] drm/i915/gvt: Update time slice more frequently

[Zhenyu Wang]

On 2018.04.04 08:43:53 +0800, Zhipeng Gong wrote:
> When there is only one vGPU in GVT-g and it submits workloads
> continuously, it will not be scheduled out, vgpu_update_timeslice
> is not called and its sched_in_time is not updated in a long time,
> which can be several seconds or longer.
> Once GVT-g pauses to submit workload for this vGPU due to heavy
> host CPU workload, this vGPU get scheduled out and
> vgpu_update_timeslice is called, its left_ts will be subtract
> by a big value from sched_out_time - sched_in_time.
> When GVT-g is going to submit workload for this vGPU again,
> it will not be scheduled in until gvt_balance_timeslice reaches
> stage 0 and reset its left_ts, which introduces several
> hunderand milliseconds latency.
> 
> This patch updates time slice in every ms to update sched_in_time
> timely.
> 
> v2: revise commit message
> v3: use more concise expr. (Zhenyu)
> 
> Signed-off-by: Zhipeng Gong <zhipeng.gong at intel.com>
> Cc: Zhenyu Wang <zhenyuw at linux.intel.com>
> Cc: Min He <min.he at intel.com>
> ---

Reviewed-by: Zhenyu Wang <zhenyuw at linux.intel.com>

btw, we might see if sched_time is wanted for statistical debug info or not later.

>  drivers/gpu/drm/i915/gvt/sched_policy.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/sched_policy.c b/drivers/gpu/drm/i915/gvt/sched_policy.c
> index 8876a57..d053cbe 100644
> --- a/drivers/gpu/drm/i915/gvt/sched_policy.c
> +++ b/drivers/gpu/drm/i915/gvt/sched_policy.c
> @@ -53,7 +53,6 @@ struct vgpu_sched_data {
>  	bool active;
>  
>  	ktime_t sched_in_time;
> -	ktime_t sched_out_time;
>  	ktime_t sched_time;
>  	ktime_t left_ts;
>  	ktime_t allocated_ts;
> @@ -69,15 +68,19 @@ struct gvt_sched_data {
>  	ktime_t expire_time;
>  };
>  
> -static void vgpu_update_timeslice(struct intel_vgpu *pre_vgpu)
> +static void vgpu_update_timeslice(struct intel_vgpu *vgpu, ktime_t cur_time)
>  {
>  	ktime_t delta_ts;
> -	struct vgpu_sched_data *vgpu_data = pre_vgpu->sched_data;
> +	struct vgpu_sched_data *vgpu_data;
>  
> -	delta_ts = vgpu_data->sched_out_time - vgpu_data->sched_in_time;
> +	if (!vgpu || vgpu == vgpu->gvt->idle_vgpu)
> +		return;
>  
> -	vgpu_data->sched_time += delta_ts;
> -	vgpu_data->left_ts -= delta_ts;
> +	vgpu_data = vgpu->sched_data;
> +	delta_ts = ktime_sub(cur_time, vgpu_data->sched_in_time);
> +	vgpu_data->sched_time = ktime_add(vgpu_data->sched_time, delta_ts);
> +	vgpu_data->left_ts = ktime_sub(vgpu_data->left_ts, delta_ts);
> +	vgpu_data->sched_in_time = cur_time;
>  }
>  
>  #define GVT_TS_BALANCE_PERIOD_MS 100
> @@ -151,11 +154,7 @@ static void try_to_schedule_next_vgpu(struct intel_gvt *gvt)
>  	}
>  
>  	cur_time = ktime_get();
> -	if (scheduler->current_vgpu) {
> -		vgpu_data = scheduler->current_vgpu->sched_data;
> -		vgpu_data->sched_out_time = cur_time;
> -		vgpu_update_timeslice(scheduler->current_vgpu);
> -	}
> +	vgpu_update_timeslice(scheduler->current_vgpu, cur_time);
>  	vgpu_data = scheduler->next_vgpu->sched_data;
>  	vgpu_data->sched_in_time = cur_time;
>  
> @@ -227,13 +226,13 @@ static void tbs_sched_func(struct gvt_sched_data *sched_data)
>  void intel_gvt_schedule(struct intel_gvt *gvt)
>  {
>  	struct gvt_sched_data *sched_data = gvt->scheduler.sched_data;
> +	ktime_t cur_time;
>  
>  	mutex_lock(&gvt->lock);
> +	cur_time = ktime_get();
>  
>  	if (test_and_clear_bit(INTEL_GVT_REQUEST_SCHED,
>  				(void *)&gvt->service_request)) {
> -		ktime_t cur_time = ktime_get();
> -
>  		if (cur_time >= sched_data->expire_time) {
>  			gvt_balance_timeslice(sched_data);
>  			sched_data->expire_time = ktime_add_ms(
> @@ -242,6 +241,7 @@ void intel_gvt_schedule(struct intel_gvt *gvt)
>  	}
>  	clear_bit(INTEL_GVT_REQUEST_EVENT_SCHED, (void *)&gvt->service_request);
>  
> +	vgpu_update_timeslice(gvt->scheduler.current_vgpu, cur_time);
>  	tbs_sched_func(sched_data);
>  
>  	mutex_unlock(&gvt->lock);
> -- 
> 2.7.4
> 

-- 
Open Source Technology Center, Intel ltd.

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