Message-ID: <20190719062442.GD28809@zhen-hp.sh.intel.com>
Date:   Fri, 19 Jul 2019 14:24:42 +0800
From:   Zhenyu Wang <zhenyuw@...ux.intel.com>
To:     Kechen Lu <kechen.lu@...el.com>
Cc:     intel-gvt-dev@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tina Zhang <tina.zhang@...el.com>,
        kraxel@...hat.com, zhenyuw@...ux.intel.com, zhiyuan.lv@...el.com,
        zhi.a.wang@...el.com, kevin.tian@...el.com, hang.yuan@...el.com,
        alex.williamson@...hat.com
Subject: Re: [RFC PATCH v4 4/6] drm/i915/gvt: Deliver vGPU refresh event to
 userspace

On 2019.07.18 23:56:38 +0800, Kechen Lu wrote:
> From: Tina Zhang <tina.zhang@...el.com>
> 
> Deliver the display refresh events to the user land. Userspace can use
> the irq mask/unmask mechanism to disable or enable the event delivery.
> 
> As we know, delivering refresh event at each vblank safely avoids
> tearing and unexpected event overwhelming, but there are still spaces
> to optimize.
> 
> For handling the normal case, deliver the page flip refresh
> event at each vblank, in other words, bounded by vblanks. Skipping some
> events bring performance enhancement while not hurting user experience.
> 
> For single framebuffer case, deliver the refresh events to userspace at
> all vblanks. This heuristic at each vblank leverages pageflip_count
> incresements to determine if there is no page flip happens after a certain
> period and so that the case is regarded as single framebuffer one.
> Although this heuristic makes incorrect decision sometimes and it depends
> on guest behavior, for example, when no cursor movements happen, the
> user experience does not harm and front buffer is still correctly acquired.
> Meanwhile, in actual single framebuffer case, the user experience is
> enhanced compared with page flip events only.
> 
> Addtionally, to mitigate the events delivering footprints, one eventfd and
> 8 byte eventfd counter partition are leveraged.
> 
> Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> Signed-off-by: Kechen Lu <kechen.lu@...el.com>
> ---
>  drivers/gpu/drm/i915/gvt/display.c |  21 ++++
>  drivers/gpu/drm/i915/gvt/gvt.h     |   7 ++
>  drivers/gpu/drm/i915/gvt/kvmgt.c   | 154 +++++++++++++++++++++++++++--
>  3 files changed, 173 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/display.c b/drivers/gpu/drm/i915/gvt/display.c
> index 1a0a4ae4826e..036db8199983 100644
> --- a/drivers/gpu/drm/i915/gvt/display.c
> +++ b/drivers/gpu/drm/i915/gvt/display.c
> @@ -387,6 +387,8 @@ void intel_gvt_check_vblank_emulation(struct intel_gvt *gvt)
>  	mutex_unlock(&gvt->lock);
>  }
>  
> +#define PAGEFLIP_INC_COUNT 5
> +
>  static void emulate_vblank_on_pipe(struct intel_vgpu *vgpu, int pipe)
>  {
>  	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
> @@ -396,7 +398,10 @@ static void emulate_vblank_on_pipe(struct intel_vgpu *vgpu, int pipe)
>  		[PIPE_B] = PIPE_B_VBLANK,
>  		[PIPE_C] = PIPE_C_VBLANK,
>  	};
> +	int pri_flip_event = SKL_FLIP_EVENT(pipe, PLANE_PRIMARY);
>  	int event;
> +	u64 eventfd_signal_val = 0;
> +	static int pageflip_count;
>  
>  	if (pipe < PIPE_A || pipe > PIPE_C)
>  		return;
> @@ -407,11 +412,27 @@ static void emulate_vblank_on_pipe(struct intel_vgpu *vgpu, int pipe)
>  		if (!pipe_is_enabled(vgpu, pipe))
>  			continue;
>  
> +		if (event == pri_flip_event) {
> +			eventfd_signal_val += DISPLAY_PRI_REFRESH_EVENT_INC;
> +			pageflip_count += PAGEFLIP_INC_COUNT;
> +		}
> +
>  		intel_vgpu_trigger_virtual_event(vgpu, event);
>  	}
>  
> +	if (--pageflip_count < 0) {
> +		eventfd_signal_val += DISPLAY_PRI_REFRESH_EVENT_INC;
> +		pageflip_count = 0;
> +	}

If pageflip_count has been increased to a big number from page flip
event for some time, then if guest switch for single buffer render, it
would take 5x vblank time to send refresh then..

> +
> +	if (vgpu->vdev.vblank_trigger && !(vgpu->vdev.display_event_mask
> +		& (DISPLAY_PRI_REFRESH_EVENT | DISPLAY_CUR_REFRESH_EVENT)) &&
> +		eventfd_signal_val)
> +		eventfd_signal(vgpu->vdev.vblank_trigger, eventfd_signal_val);
> +
>  	if (pipe_is_enabled(vgpu, pipe)) {
>  		vgpu_vreg_t(vgpu, PIPE_FRMCOUNT_G4X(pipe))++;
> +
>  		intel_vgpu_trigger_virtual_event(vgpu, vblank_event[pipe]);
>  	}
>  }
> diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
> index 64d1c1aaa42a..b654b6fa0663 100644
> --- a/drivers/gpu/drm/i915/gvt/gvt.h
> +++ b/drivers/gpu/drm/i915/gvt/gvt.h
> @@ -165,6 +165,11 @@ struct intel_vgpu_submission {
>  	bool active;
>  };
>  
> +#define DISPLAY_PRI_REFRESH_EVENT	(1 << 0)
> +#define DISPLAY_PRI_REFRESH_EVENT_INC	(1UL << 56)
> +#define DISPLAY_CUR_REFRESH_EVENT	(1 << 1)
> +#define DISPLAY_CUR_REFRESH_EVENT_INC	(1UL << 48)
> +

As this is for eventfd interface definition, need to put in vfio header instead of gvt's,
as this is userspace API. And better reorder for different usage on irq masking and eventfd value.

For eventfd value, this looks like counter for each plane? Or do we just need a flag?

>  struct intel_vgpu {
>  	struct intel_gvt *gvt;
>  	struct mutex vgpu_lock;
> @@ -205,6 +210,8 @@ struct intel_vgpu {
>  		int num_irqs;
>  		struct eventfd_ctx *intx_trigger;
>  		struct eventfd_ctx *msi_trigger;
> +		struct eventfd_ctx *vblank_trigger;
> +		u32 display_event_mask;
>  
>  		/*
>  		 * Two caches are used to avoid mapping duplicated pages (eg.
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 6fe825763d05..61c634618217 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -1222,6 +1222,8 @@ static int intel_vgpu_get_irq_count(struct intel_vgpu *vgpu, int type)
>  {
>  	if (type == VFIO_PCI_INTX_IRQ_INDEX || type == VFIO_PCI_MSI_IRQ_INDEX)
>  		return 1;
> +	else if (type < VFIO_PCI_NUM_IRQS + vgpu->vdev.num_irqs)
> +		return vgpu->vdev.irq[type - VFIO_PCI_NUM_IRQS].count;
>  
>  	return 0;
>  }
> @@ -1269,7 +1271,62 @@ static int intel_vgpu_set_msi_trigger(struct intel_vgpu *vgpu,
>  	return 0;
>  }
>  
> -static int intel_vgpu_set_irqs(struct intel_vgpu *vgpu, u32 flags,
> +static int intel_vgu_set_display_irq_mask(struct intel_vgpu *vgpu,
> +		unsigned int index, unsigned int start, unsigned int count,
> +		u32 flags, void *data)
> +{
> +	if (start != 0 || count > 2)
> +		return -EINVAL;
> +
> +	if (flags & VFIO_IRQ_SET_DATA_NONE)
> +		vgpu->vdev.display_event_mask |= DISPLAY_PRI_REFRESH_EVENT |
> +			DISPLAY_CUR_REFRESH_EVENT;
> +
> +	return 0;
> +}
> +
> +static int intel_vgu_set_display_irq_unmask(struct intel_vgpu *vgpu,
> +		unsigned int index, unsigned int start, unsigned int count,
> +		u32 flags, void *data)
> +{
> +	if (start != 0 || count > 2)
> +		return -EINVAL;
> +
> +	if (flags & VFIO_IRQ_SET_DATA_NONE)
> +		vgpu->vdev.display_event_mask &= ~(DISPLAY_PRI_REFRESH_EVENT |
> +			   DISPLAY_CUR_REFRESH_EVENT);
> +
> +	return 0;
> +}
> +
> +static int intel_vgpu_set_display_event_trigger(struct intel_vgpu *vgpu,
> +		unsigned int index, unsigned int start, unsigned int count,
> +		u32 flags, void *data)
> +{
> +	struct eventfd_ctx *trigger;
> +
> +	if (flags & VFIO_IRQ_SET_DATA_EVENTFD) {
> +		int fd = *(int *)data;
> +
> +		trigger = eventfd_ctx_fdget(fd);
> +		if (IS_ERR(trigger)) {
> +			gvt_vgpu_err("eventfd_ctx_fdget failed\n");
> +			return PTR_ERR(trigger);
> +		}
> +		vgpu->vdev.vblank_trigger = trigger;
> +		vgpu->vdev.display_event_mask = 0;
> +	} else if ((flags & VFIO_IRQ_SET_DATA_NONE) && !count) {
> +		trigger = vgpu->vdev.vblank_trigger;
> +		if (trigger) {
> +			eventfd_ctx_put(trigger);
> +			vgpu->vdev.vblank_trigger = NULL;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +int intel_vgpu_set_irqs(struct intel_vgpu *vgpu, u32 flags,
>  		unsigned int index, unsigned int start, unsigned int count,
>  		void *data)
>  {
> @@ -1302,6 +1359,35 @@ static int intel_vgpu_set_irqs(struct intel_vgpu *vgpu, u32 flags,
>  			break;
>  		}
>  		break;
> +	default:
> +	{
> +		int i;
> +
> +		if (index >= VFIO_PCI_NUM_IRQS +
> +					vgpu->vdev.num_irqs)
> +			return -EINVAL;
> +		index =
> +			array_index_nospec(index,
> +						VFIO_PCI_NUM_IRQS +
> +						vgpu->vdev.num_irqs);
> +
> +		i = index - VFIO_PCI_NUM_IRQS;
> +		if (vgpu->vdev.irq[i].type == VFIO_IRQ_TYPE_GFX &&
> +		    vgpu->vdev.irq[i].subtype ==
> +		    VFIO_IRQ_SUBTYPE_GFX_DISPLAY_IRQ) {
> +			switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
> +			case VFIO_IRQ_SET_ACTION_MASK:
> +				func = intel_vgu_set_display_irq_mask;
> +				break;
> +			case VFIO_IRQ_SET_ACTION_UNMASK:
> +				func = intel_vgu_set_display_irq_unmask;
> +				break;
> +			case VFIO_IRQ_SET_ACTION_TRIGGER:
> +				func = intel_vgpu_set_display_event_trigger;
> +				break;
> +			}
> +		}
> +	}
>  	}
>  
>  	if (!func)
> @@ -1333,7 +1419,7 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  		info.flags |= VFIO_DEVICE_FLAGS_RESET;
>  		info.num_regions = VFIO_PCI_NUM_REGIONS +
>  				vgpu->vdev.num_regions;
> -		info.num_irqs = VFIO_PCI_NUM_IRQS;
> +		info.num_irqs = VFIO_PCI_NUM_IRQS + vgpu->vdev.num_irqs;
>  
>  		return copy_to_user((void __user *)arg, &info, minsz) ?
>  			-EFAULT : 0;
> @@ -1493,32 +1579,81 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  			-EFAULT : 0;
>  	} else if (cmd == VFIO_DEVICE_GET_IRQ_INFO) {
>  		struct vfio_irq_info info;
> +		struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
> +		unsigned int i;
> +		int ret;
>  
>  		minsz = offsetofend(struct vfio_irq_info, count);
>  
>  		if (copy_from_user(&info, (void __user *)arg, minsz))
>  			return -EFAULT;
>  
> -		if (info.argsz < minsz || info.index >= VFIO_PCI_NUM_IRQS)
> +		if (info.argsz < minsz)
>  			return -EINVAL;
>  
>  		switch (info.index) {
>  		case VFIO_PCI_INTX_IRQ_INDEX:
>  		case VFIO_PCI_MSI_IRQ_INDEX:
> +			info.flags = VFIO_IRQ_INFO_EVENTFD;
>  			break;
> -		default:
> +		case VFIO_PCI_MSIX_IRQ_INDEX:
> +		case VFIO_PCI_ERR_IRQ_INDEX:
> +		case VFIO_PCI_REQ_IRQ_INDEX:
>  			return -EINVAL;
> -		}
> +		default:
> +		{
> +			struct vfio_irq_info_cap_type cap_type = {
> +				.header.id = VFIO_IRQ_INFO_CAP_TYPE,
> +				.header.version = 1 };
>  
> -		info.flags = VFIO_IRQ_INFO_EVENTFD;
> +			if (info.index >= VFIO_PCI_NUM_IRQS +
> +					vgpu->vdev.num_irqs)
> +				return -EINVAL;
> +			info.index =
> +				array_index_nospec(info.index,
> +						VFIO_PCI_NUM_IRQS +
> +						vgpu->vdev.num_irqs);
> +
> +			i = info.index - VFIO_PCI_NUM_IRQS;
> +
> +			info.flags = vgpu->vdev.irq[i].flags;
> +			cap_type.type = vgpu->vdev.irq[i].type;
> +			cap_type.subtype = vgpu->vdev.irq[i].subtype;
> +
> +			ret = vfio_info_add_capability(&caps,
> +						&cap_type.header,
> +						sizeof(cap_type));
> +			if (ret)
> +				return ret;
> +		}
> +		}
>  
>  		info.count = intel_vgpu_get_irq_count(vgpu, info.index);
>  
>  		if (info.index == VFIO_PCI_INTX_IRQ_INDEX)
>  			info.flags |= (VFIO_IRQ_INFO_MASKABLE |
>  				       VFIO_IRQ_INFO_AUTOMASKED);
> -		else
> -			info.flags |= VFIO_IRQ_INFO_NORESIZE;
> +
> +		if (caps.size) {
> +			info.flags |= VFIO_IRQ_INFO_FLAG_CAPS;
> +			if (info.argsz < sizeof(info) + caps.size) {
> +				info.argsz = sizeof(info) + caps.size;
> +				info.cap_offset = 0;
> +			} else {
> +				vfio_info_cap_shift(&caps, sizeof(info));
> +				if (copy_to_user((void __user *)arg +
> +						  sizeof(info), caps.buf,
> +						  caps.size)) {
> +					kfree(caps.buf);
> +					return -EFAULT;
> +				}
> +				info.cap_offset = sizeof(info);
> +				if (offsetofend(struct vfio_irq_info, cap_offset) > minsz)
> +					minsz = offsetofend(struct vfio_irq_info, cap_offset);
> +			}
> +
> +			kfree(caps.buf);
> +		}
>  
>  		return copy_to_user((void __user *)arg, &info, minsz) ?
>  			-EFAULT : 0;
> @@ -1537,7 +1672,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  			int max = intel_vgpu_get_irq_count(vgpu, hdr.index);
>  
>  			ret = vfio_set_irqs_validate_and_prepare(&hdr, max,
> -						VFIO_PCI_NUM_IRQS, &data_size);
> +					VFIO_PCI_NUM_IRQS + vgpu->vdev.num_irqs,
> +								 &data_size);
>  			if (ret) {
>  				gvt_vgpu_err("intel:vfio_set_irqs_validate_and_prepare failed\n");
>  				return -EINVAL;
> -- 
> 2.17.1
> 

-- 
Open Source Technology Center, Intel ltd.

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