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* [PATHC v2] video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver
@ 2019-08-27 11:25 Wei Hu
  2019-08-28  0:07 ` Michael Kelley
  0 siblings, 1 reply; 3+ messages in thread
From: Wei Hu @ 2019-08-27 11:25 UTC (permalink / raw)
  To: rdunlap, shc_work, gregkh, lee.jones, alexandre.belloni,
	baijiaju1990, fthain, info, linux-hyperv, dri-devel, linux-fbdev,
	linux-kernel, sashal, Stephen Hemminger, Haiyang Zhang,
	KY Srinivasan, Dexuan Cui, Michael Kelley
  Cc: Wei Hu

Without deferred IO support, hyperv_fb driver informs the host to refresh
the entire guest frame buffer at fixed rate, e.g. at 20Hz, no matter there
is screen update or not. This patch supports deferred IO for screens in
graphics mode and also enables the frame buffer on-demand refresh. The
highest refresh rate is still set at 20Hz.

Currently Hyper-V only takes a physical address from guest as the starting
address of frame buffer. This implies the guest must allocate contiguous
physical memory for frame buffer. In addition, Hyper-V Gen 2 VMs only
accept address from MMIO region as frame buffer address. Due to these
limitations on Hyper-V host, we keep a shadow copy of frame buffer
in the guest. This means one more copy of the dirty rectangle inside
guest when doing the on-demand refresh. This can be optimized in the
future with help from host. For now the host performance gain from deferred
IO outweighs the shadow copy impact in the guest.

v2: Incorporated review comments from Michael Kelley
- Increased dirty rectangle by one row in deferred IO case when sending
to Hyper-V.
- Corrected the dirty rectangle size in the text mode.
- Added more comments.
- Other minor code cleanups.

Signed-off-by: Wei Hu <weh@microsoft.com>
---
 drivers/video/fbdev/Kconfig     |   1 +
 drivers/video/fbdev/hyperv_fb.c | 221 +++++++++++++++++++++++++++++---
 2 files changed, 202 insertions(+), 20 deletions(-)

diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
index 1b2f5f31fb6f..e781f89a1824 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -2241,6 +2241,7 @@ config FB_HYPERV
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FB_DEFERRED_IO
 	help
 	  This framebuffer driver supports Microsoft Hyper-V Synthetic Video.
 
diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index 2ca400c0d621..279a2164a57c 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -234,6 +234,7 @@ struct synthvid_msg {
 #define RING_BUFSIZE (256 * 1024)
 #define VSP_TIMEOUT (10 * HZ)
 #define HVFB_UPDATE_DELAY (HZ / 20)
+#define HVFB_ONDEMAND_THROTTLE (HZ / 20)
 
 struct hvfb_par {
 	struct fb_info *info;
@@ -253,6 +254,17 @@ struct hvfb_par {
 	bool synchronous_fb;
 
 	struct notifier_block hvfb_panic_nb;
+
+	/* Memory for deferred IO and frame buffer itself */
+	unsigned char *dio_vp;
+	unsigned char *mmio_vp;
+	unsigned long mmio_pp;
+	spinlock_t docopy_lock; /* Lock to protect memory copy */
+
+	/* Dirty rectangle, protected by delayed_refresh_lock */
+	int x1, y1, x2, y2;
+	bool delayed_refresh;
+	spinlock_t delayed_refresh_lock;
 };
 
 static uint screen_width = HVFB_WIDTH;
@@ -261,6 +273,7 @@ static uint screen_width_max = HVFB_WIDTH;
 static uint screen_height_max = HVFB_HEIGHT;
 static uint screen_depth;
 static uint screen_fb_size;
+static uint dio_fb_size; /* FB size for deferred IO */
 
 /* Send message to Hyper-V host */
 static inline int synthvid_send(struct hv_device *hdev,
@@ -347,28 +360,94 @@ static int synthvid_send_ptr(struct hv_device *hdev)
 }
 
 /* Send updated screen area (dirty rectangle) location to host */
-static int synthvid_update(struct fb_info *info)
+static int
+synthvid_update(struct fb_info *info, int x1, int y1, int x2, int y2)
 {
 	struct hv_device *hdev = device_to_hv_device(info->device);
 	struct synthvid_msg msg;
 
 	memset(&msg, 0, sizeof(struct synthvid_msg));
+	if (x2 == INT_MAX)
+		x2 = info->var.xres;
+	if (y2 == INT_MAX)
+		y2 = info->var.yres;
 
 	msg.vid_hdr.type = SYNTHVID_DIRT;
 	msg.vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
 		sizeof(struct synthvid_dirt);
 	msg.dirt.video_output = 0;
 	msg.dirt.dirt_count = 1;
-	msg.dirt.rect[0].x1 = 0;
-	msg.dirt.rect[0].y1 = 0;
-	msg.dirt.rect[0].x2 = info->var.xres;
-	msg.dirt.rect[0].y2 = info->var.yres;
+	msg.dirt.rect[0].x1 = (x1 > x2) ? 0 : x1;
+	msg.dirt.rect[0].y1 = (y1 > y2) ? 0 : y1;
+	msg.dirt.rect[0].x2 =
+		(x2 < x1 || x2 > info->var.xres) ? info->var.xres : x2;
+	msg.dirt.rect[0].y2 =
+		(y2 < y1 || y2 > info->var.yres) ? info->var.yres : y2;
 
 	synthvid_send(hdev, &msg);
 
 	return 0;
 }
 
+static void hvfb_docopy(struct hvfb_par *par,
+			unsigned long offset,
+			unsigned long size)
+{
+	if (!par || !par->mmio_vp || !par->dio_vp || !par->fb_ready ||
+	    size == 0 || offset >= dio_fb_size)
+		return;
+
+	if (offset + size > dio_fb_size)
+		size = dio_fb_size - offset;
+
+	memcpy(par->mmio_vp + offset, par->dio_vp + offset, size);
+}
+
+/* Deferred IO callback */
+static void synthvid_deferred_io(struct fb_info *p,
+				 struct list_head *pagelist)
+{
+	struct hvfb_par *par = p->par;
+	struct page *page;
+	unsigned long start, end;
+	int y1, y2, miny, maxy;
+	unsigned long flags;
+
+	miny = INT_MAX;
+	maxy = 0;
+
+	/*
+	 * Merge dirty pages. It is possible that last page cross
+	 * over the end of frame buffer row yres. This is taken care of
+	 * in synthvid_update function by clamping the y2
+	 * value to yres.
+	 */
+	list_for_each_entry(page, pagelist, lru) {
+		start = page->index << PAGE_SHIFT;
+		end = start + PAGE_SIZE - 1;
+		y1 = start / p->fix.line_length;
+		y2 = end / p->fix.line_length;
+		if (y2 > p->var.yres)
+			y2 = p->var.yres;
+		miny = min_t(int, miny, y1);
+		maxy = max_t(int, maxy, y2);
+
+		/* Copy from dio space to mmio address */
+		if (par->fb_ready) {
+			spin_lock_irqsave(&par->docopy_lock, flags);
+			hvfb_docopy(par, start, PAGE_SIZE);
+			spin_unlock_irqrestore(&par->docopy_lock, flags);
+		}
+	}
+
+	if (par->fb_ready)
+		synthvid_update(p, 0, miny, p->var.xres, maxy + 1);
+}
+
+static struct fb_deferred_io synthvid_defio = {
+	.delay		= HZ / 20,
+	.deferred_io	= synthvid_deferred_io,
+};
 
 /*
  * Actions on received messages from host:
@@ -604,7 +683,7 @@ static int synthvid_send_config(struct hv_device *hdev)
 	msg->vid_hdr.type = SYNTHVID_VRAM_LOCATION;
 	msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
 		sizeof(struct synthvid_vram_location);
-	msg->vram.user_ctx = msg->vram.vram_gpa = info->fix.smem_start;
+	msg->vram.user_ctx = msg->vram.vram_gpa = par->mmio_pp;
 	msg->vram.is_vram_gpa_specified = 1;
 	synthvid_send(hdev, msg);
 
@@ -614,7 +693,7 @@ static int synthvid_send_config(struct hv_device *hdev)
 		ret = -ETIMEDOUT;
 		goto out;
 	}
-	if (msg->vram_ack.user_ctx != info->fix.smem_start) {
+	if (msg->vram_ack.user_ctx != par->mmio_pp) {
 		pr_err("Unable to set VRAM location\n");
 		ret = -ENODEV;
 		goto out;
@@ -631,19 +710,82 @@ static int synthvid_send_config(struct hv_device *hdev)
 
 /*
  * Delayed work callback:
- * It is called at HVFB_UPDATE_DELAY or longer time interval to process
- * screen updates. It is re-scheduled if further update is necessary.
+ * It is scheduled to call whenever update request is received and it has
+ * not been called in last HVFB_ONDEMAND_THROTTLE time interval.
  */
 static void hvfb_update_work(struct work_struct *w)
 {
 	struct hvfb_par *par = container_of(w, struct hvfb_par, dwork.work);
 	struct fb_info *info = par->info;
+	unsigned long flags;
+	int x1, x2, y1, y2;
+	int j;
+
+	spin_lock_irqsave(&par->delayed_refresh_lock, flags);
+	/* Reset the request flag */
+	par->delayed_refresh = false;
+
+	/* Store the dirty rectangle to local variables */
+	x1 = par->x1;
+	x2 = par->x2;
+	y1 = par->y1;
+	y2 = par->y2;
+
+	/* Clear dirty rectangle */
+	par->x1 = par->y1 = INT_MAX;
+	par->x2 = par->y2 = 0;
+
+	spin_unlock_irqrestore(&par->delayed_refresh_lock, flags);
 
+	if (x1 < 0 || x1 > info->var.xres || x2 < 0 ||
+	    x2 > info->var.xres || y1 < 0 || y1 > info->var.yres ||
+	    y2 < 0 || y2 > info->var.yres || x2 <= x1)
+		return;
+
+	/* Copy the dirty rectangle to frame buffer memory */
+	spin_lock_irqsave(&par->docopy_lock, flags);
+	for (j = y1; j < y2; j++) {
+		if (j == info->var.yres)
+			break;
+		hvfb_docopy(par,
+			    j * info->fix.line_length +
+			    (x1 * screen_depth / 8),
+			    (x2 - x1) * screen_depth / 8);
+	}
+	spin_unlock_irqrestore(&par->docopy_lock, flags);
+
+	/* Refresh */
 	if (par->fb_ready)
-		synthvid_update(info);
+		synthvid_update(info, x1, y1, x2, y2);
+}
+
+/*
+ * Control the on-demand refresh frequency. It schedules a delayed
+ * screen update if it has not yet.
+ */
+static void hvfb_ondemand_refresh_throttle(struct hvfb_par *par,
+					   int x1, int y1, int w, int h)
+{
+	unsigned long flags;
+	int x2 = x1 + w;
+	int y2 = y1 + h;
+
+	spin_lock_irqsave(&par->delayed_refresh_lock, flags);
+
+	/* Merge dirty rectangle */
+	par->x1 = min_t(int, par->x1, x1);
+	par->y1 = min_t(int, par->y1, y1);
+	par->x2 = max_t(int, par->x2, x2);
+	par->y2 = max_t(int, par->y2, y2);
+
+	/* Schedule a delayed screen update if not yet */
+	if (par->delayed_refresh == false) {
+		schedule_delayed_work(&par->dwork,
+				      HVFB_ONDEMAND_THROTTLE);
+		par->delayed_refresh = true;
+	}
 
-	if (par->update)
-		schedule_delayed_work(&par->dwork, HVFB_UPDATE_DELAY);
+	spin_unlock_irqrestore(&par->delayed_refresh_lock, flags);
 }
 
 static int hvfb_on_panic(struct notifier_block *nb,
@@ -655,7 +797,8 @@ static int hvfb_on_panic(struct notifier_block *nb,
 	par = container_of(nb, struct hvfb_par, hvfb_panic_nb);
 	par->synchronous_fb = true;
 	info = par->info;
-	synthvid_update(info);
+	hvfb_docopy(par, 0, dio_fb_size);
+	synthvid_update(info, 0, 0, INT_MAX, INT_MAX);
 
 	return NOTIFY_DONE;
 }
@@ -716,7 +859,10 @@ static void hvfb_cfb_fillrect(struct fb_info *p,
 
 	cfb_fillrect(p, rect);
 	if (par->synchronous_fb)
-		synthvid_update(p);
+		synthvid_update(p, 0, 0, INT_MAX, INT_MAX);
+	else
+		hvfb_ondemand_refresh_throttle(par, rect->dx, rect->dy,
+					       rect->width, rect->height);
 }
 
 static void hvfb_cfb_copyarea(struct fb_info *p,
@@ -726,7 +872,10 @@ static void hvfb_cfb_copyarea(struct fb_info *p,
 
 	cfb_copyarea(p, area);
 	if (par->synchronous_fb)
-		synthvid_update(p);
+		synthvid_update(p, 0, 0, INT_MAX, INT_MAX);
+	else
+		hvfb_ondemand_refresh_throttle(par, area->dx, area->dy,
+					       area->width, area->height);
 }
 
 static void hvfb_cfb_imageblit(struct fb_info *p,
@@ -736,7 +885,10 @@ static void hvfb_cfb_imageblit(struct fb_info *p,
 
 	cfb_imageblit(p, image);
 	if (par->synchronous_fb)
-		synthvid_update(p);
+		synthvid_update(p, 0, 0, INT_MAX, INT_MAX);
+	else
+		hvfb_ondemand_refresh_throttle(par, image->dx, image->dy,
+					       image->width, image->height);
 }
 
 static struct fb_ops hvfb_ops = {
@@ -795,6 +947,9 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 	resource_size_t pot_start, pot_end;
 	int ret;
 
+	dio_fb_size =
+		screen_width * screen_height * screen_depth / 8;
+
 	if (gen2vm) {
 		pot_start = 0;
 		pot_end = -1;
@@ -829,9 +984,14 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 	if (!fb_virt)
 		goto err2;
 
+	/* Allocate memory for deferred IO */
+	par->dio_vp = vzalloc(round_up(dio_fb_size, PAGE_SIZE));
+	if (par->dio_vp == NULL)
+		goto err3;
+
 	info->apertures = alloc_apertures(1);
 	if (!info->apertures)
-		goto err3;
+		goto err4;
 
 	if (gen2vm) {
 		info->apertures->ranges[0].base = screen_info.lfb_base;
@@ -843,16 +1003,23 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 		info->apertures->ranges[0].size = pci_resource_len(pdev, 0);
 	}
 
+	/* Physical address of FB device */
+	par->mmio_pp = par->mem->start;
+	/* Virtual address of FB device */
+	par->mmio_vp = (unsigned char *) fb_virt;
+
 	info->fix.smem_start = par->mem->start;
-	info->fix.smem_len = screen_fb_size;
-	info->screen_base = fb_virt;
-	info->screen_size = screen_fb_size;
+	info->fix.smem_len = dio_fb_size;
+	info->screen_base = par->dio_vp;
+	info->screen_size = dio_fb_size;
 
 	if (!gen2vm)
 		pci_dev_put(pdev);
 
 	return 0;
 
+err4:
+	vfree(par->dio_vp);
 err3:
 	iounmap(fb_virt);
 err2:
@@ -870,6 +1037,7 @@ static void hvfb_putmem(struct fb_info *info)
 {
 	struct hvfb_par *par = info->par;
 
+	vfree(par->dio_vp);
 	iounmap(info->screen_base);
 	vmbus_free_mmio(par->mem->start, screen_fb_size);
 	par->mem = NULL;
@@ -895,6 +1063,12 @@ static int hvfb_probe(struct hv_device *hdev,
 	init_completion(&par->wait);
 	INIT_DELAYED_WORK(&par->dwork, hvfb_update_work);
 
+	par->delayed_refresh = false;
+	spin_lock_init(&par->delayed_refresh_lock);
+	spin_lock_init(&par->docopy_lock);
+	par->x1 = par->y1 = INT_MAX;
+	par->x2 = par->y2 = 0;
+
 	/* Connect to VSP */
 	hv_set_drvdata(hdev, info);
 	ret = synthvid_connect_vsp(hdev);
@@ -946,6 +1120,10 @@ static int hvfb_probe(struct hv_device *hdev,
 	info->fbops = &hvfb_ops;
 	info->pseudo_palette = par->pseudo_palette;
 
+	/* Initialize deferred IO */
+	info->fbdefio = &synthvid_defio;
+	fb_deferred_io_init(info);
+
 	/* Send config to host */
 	ret = synthvid_send_config(hdev);
 	if (ret)
@@ -967,6 +1145,7 @@ static int hvfb_probe(struct hv_device *hdev,
 	return 0;
 
 error:
+	fb_deferred_io_cleanup(info);
 	hvfb_putmem(info);
 error2:
 	vmbus_close(hdev->channel);
@@ -989,6 +1168,8 @@ static int hvfb_remove(struct hv_device *hdev)
 	par->update = false;
 	par->fb_ready = false;
 
+	fb_deferred_io_cleanup(info);
+
 	unregister_framebuffer(info);
 	cancel_delayed_work_sync(&par->dwork);
 
-- 
2.20.1


^ permalink raw reply	[flat|nested] 3+ messages in thread

* RE: [PATHC v2] video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver
  2019-08-27 11:25 [PATHC v2] video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver Wei Hu
@ 2019-08-28  0:07 ` Michael Kelley
  2019-08-28  9:12   ` Wei Hu
  0 siblings, 1 reply; 3+ messages in thread
From: Michael Kelley @ 2019-08-28  0:07 UTC (permalink / raw)
  To: Wei Hu, rdunlap, shc_work, gregkh, lee.jones, alexandre.belloni,
	baijiaju1990, fthain, info, linux-hyperv, dri-devel, linux-fbdev,
	linux-kernel, sashal, Stephen Hemminger, Haiyang Zhang,
	KY Srinivasan, Dexuan Cui

From: Wei Hu <weh@microsoft.com>  Sent: Tuesday, August 27, 2019 4:25 AM
> 
> Without deferred IO support, hyperv_fb driver informs the host to refresh
> the entire guest frame buffer at fixed rate, e.g. at 20Hz, no matter there
> is screen update or not. This patch supports deferred IO for screens in
> graphics mode and also enables the frame buffer on-demand refresh. The
> highest refresh rate is still set at 20Hz.
> 
> Currently Hyper-V only takes a physical address from guest as the starting
> address of frame buffer. This implies the guest must allocate contiguous
> physical memory for frame buffer. In addition, Hyper-V Gen 2 VMs only
> accept address from MMIO region as frame buffer address. Due to these
> limitations on Hyper-V host, we keep a shadow copy of frame buffer
> in the guest. This means one more copy of the dirty rectangle inside
> guest when doing the on-demand refresh. This can be optimized in the
> future with help from host. For now the host performance gain from deferred
> IO outweighs the shadow copy impact in the guest.
> 
> v2: Incorporated review comments from Michael Kelley
> - Increased dirty rectangle by one row in deferred IO case when sending
> to Hyper-V.
> - Corrected the dirty rectangle size in the text mode.
> - Added more comments.
> - Other minor code cleanups.

Version history should go after the "---" below so it is not included in
the commit message.

> 
> Signed-off-by: Wei Hu <weh@microsoft.com>
> ---
>  drivers/video/fbdev/Kconfig     |   1 +
>  drivers/video/fbdev/hyperv_fb.c | 221 +++++++++++++++++++++++++++++---
>  2 files changed, 202 insertions(+), 20 deletions(-)
> 
> +/* Deferred IO callback */
> +static void synthvid_deferred_io(struct fb_info *p,
> +				 struct list_head *pagelist)
> +{
> +	struct hvfb_par *par = p->par;
> +	struct page *page;
> +	unsigned long start, end;
> +	int y1, y2, miny, maxy;
> +	unsigned long flags;
> +
> +	miny = INT_MAX;
> +	maxy = 0;
> +
> +	/*
> +	 * Merge dirty pages. It is possible that last page cross
> +	 * over the end of frame buffer row yres. This is taken care of
> +	 * in synthvid_update function by clamping the y2
> +	 * value to yres.
> +	 */
> +	list_for_each_entry(page, pagelist, lru) {
> +		start = page->index << PAGE_SHIFT;
> +		end = start + PAGE_SIZE - 1;
> +		y1 = start / p->fix.line_length;
> +		y2 = end / p->fix.line_length;
> +		if (y2 > p->var.yres)
> +			y2 = p->var.yres;

The above test seems contradictory to the comment that
says the clamping is done in synthvid_update().  Also, since
the above calculation of y2 is "inclusive", the clamping should
be done to yres - 1 in order to continue to be inclusive.  Then
when maxy + 1 is passed to synthvid_update() everything works
out correctly.

> +		miny = min_t(int, miny, y1);
> +		maxy = max_t(int, maxy, y2);
> +
> +		/* Copy from dio space to mmio address */
> +		if (par->fb_ready) {
> +			spin_lock_irqsave(&par->docopy_lock, flags);
> +			hvfb_docopy(par, start, PAGE_SIZE);
> +			spin_unlock_irqrestore(&par->docopy_lock, flags);
> +		}
> +	}
> +
> +	if (par->fb_ready)
> +		synthvid_update(p, 0, miny, p->var.xres, maxy + 1);
> +}
> +
> +static struct fb_deferred_io synthvid_defio = {
> +	.delay		= HZ / 20,
> +	.deferred_io	= synthvid_deferred_io,
> +};
> 
>  /*
>   * Actions on received messages from host:
> @@ -604,7 +683,7 @@ static int synthvid_send_config(struct hv_device *hdev)
>  	msg->vid_hdr.type = SYNTHVID_VRAM_LOCATION;
>  	msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
>  		sizeof(struct synthvid_vram_location);
> -	msg->vram.user_ctx = msg->vram.vram_gpa = info->fix.smem_start;
> +	msg->vram.user_ctx = msg->vram.vram_gpa = par->mmio_pp;
>  	msg->vram.is_vram_gpa_specified = 1;
>  	synthvid_send(hdev, msg);
> 
> @@ -614,7 +693,7 @@ static int synthvid_send_config(struct hv_device *hdev)
>  		ret = -ETIMEDOUT;
>  		goto out;
>  	}
> -	if (msg->vram_ack.user_ctx != info->fix.smem_start) {
> +	if (msg->vram_ack.user_ctx != par->mmio_pp) {
>  		pr_err("Unable to set VRAM location\n");
>  		ret = -ENODEV;
>  		goto out;
> @@ -631,19 +710,82 @@ static int synthvid_send_config(struct hv_device *hdev)
> 
>  /*
>   * Delayed work callback:
> - * It is called at HVFB_UPDATE_DELAY or longer time interval to process
> - * screen updates. It is re-scheduled if further update is necessary.
> + * It is scheduled to call whenever update request is received and it has
> + * not been called in last HVFB_ONDEMAND_THROTTLE time interval.
>   */
>  static void hvfb_update_work(struct work_struct *w)
>  {
>  	struct hvfb_par *par = container_of(w, struct hvfb_par, dwork.work);
>  	struct fb_info *info = par->info;
> +	unsigned long flags;
> +	int x1, x2, y1, y2;
> +	int j;
> +
> +	spin_lock_irqsave(&par->delayed_refresh_lock, flags);
> +	/* Reset the request flag */
> +	par->delayed_refresh = false;
> +
> +	/* Store the dirty rectangle to local variables */
> +	x1 = par->x1;
> +	x2 = par->x2;
> +	y1 = par->y1;
> +	y2 = par->y2;
> +
> +	/* Clear dirty rectangle */
> +	par->x1 = par->y1 = INT_MAX;
> +	par->x2 = par->y2 = 0;
> +
> +	spin_unlock_irqrestore(&par->delayed_refresh_lock, flags);
> 
> +	if (x1 < 0 || x1 > info->var.xres || x2 < 0 ||
> +	    x2 > info->var.xres || y1 < 0 || y1 > info->var.yres ||
> +	    y2 < 0 || y2 > info->var.yres || x2 <= x1)
> +		return;

Are the tests for less than 0 needed?  I think all possibility of
negative values has been eliminated.

> +
> +	/* Copy the dirty rectangle to frame buffer memory */
> +	spin_lock_irqsave(&par->docopy_lock, flags);
> +	for (j = y1; j < y2; j++) {
> +		if (j == info->var.yres)
> +			break;

The above test isn't needed.  The maximum value that y2 can be
is yres (that is checked a few lines above in the big "if" statement).
Since j is always less than y2, j can never be equal to yres.

> +		hvfb_docopy(par,
> +			    j * info->fix.line_length +
> +			    (x1 * screen_depth / 8),
> +			    (x2 - x1) * screen_depth / 8);
> +	}
> +	spin_unlock_irqrestore(&par->docopy_lock, flags);
> +
> +	/* Refresh */
>  	if (par->fb_ready)
> -		synthvid_update(info);
> +		synthvid_update(info, x1, y1, x2, y2);
> +}
> +

Michael

^ permalink raw reply	[flat|nested] 3+ messages in thread

* RE: [PATHC v2] video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver
  2019-08-28  0:07 ` Michael Kelley
@ 2019-08-28  9:12   ` Wei Hu
  0 siblings, 0 replies; 3+ messages in thread
From: Wei Hu @ 2019-08-28  9:12 UTC (permalink / raw)
  To: Michael Kelley, rdunlap, shc_work, gregkh, lee.jones,
	alexandre.belloni, baijiaju1990, fthain, info, linux-hyperv,
	dri-devel, linux-fbdev, linux-kernel, sashal, Stephen Hemminger,
	Haiyang Zhang, KY Srinivasan, Dexuan Cui



> -----Original Message-----
> From: Michael Kelley <mikelley@microsoft.com>
> 
> From: Wei Hu <weh@microsoft.com>  Sent: Tuesday, August 27, 2019 4:25 AM
> >
> > Without deferred IO support, hyperv_fb driver informs the host to refresh
> > the entire guest frame buffer at fixed rate, e.g. at 20Hz, no matter there
> > is screen update or not. This patch supports deferred IO for screens in
> > graphics mode and also enables the frame buffer on-demand refresh. The
> > highest refresh rate is still set at 20Hz.
> >
> > Currently Hyper-V only takes a physical address from guest as the starting
> > address of frame buffer. This implies the guest must allocate contiguous
> > physical memory for frame buffer. In addition, Hyper-V Gen 2 VMs only
> > accept address from MMIO region as frame buffer address. Due to these
> > limitations on Hyper-V host, we keep a shadow copy of frame buffer
> > in the guest. This means one more copy of the dirty rectangle inside
> > guest when doing the on-demand refresh. This can be optimized in the
> > future with help from host. For now the host performance gain from deferred
> > IO outweighs the shadow copy impact in the guest.
> >
> > v2: Incorporated review comments from Michael Kelley
> > - Increased dirty rectangle by one row in deferred IO case when sending
> > to Hyper-V.
> > - Corrected the dirty rectangle size in the text mode.
> > - Added more comments.
> > - Other minor code cleanups.
> 
> Version history should go after the "---" below so it is not included in
> the commit message.
> 
[Wei Hu] 
I saw version history in the commit logs. 

> >
> > Signed-off-by: Wei Hu <weh@microsoft.com>
> > ---
> >  drivers/video/fbdev/Kconfig     |   1 +
> >  drivers/video/fbdev/hyperv_fb.c | 221 +++++++++++++++++++++++++++++---
> >  2 files changed, 202 insertions(+), 20 deletions(-)
> >
> > +/* Deferred IO callback */
> > +static void synthvid_deferred_io(struct fb_info *p,
> > +				 struct list_head *pagelist)
> > +{
> > +	struct hvfb_par *par = p->par;
> > +	struct page *page;
> > +	unsigned long start, end;
> > +	int y1, y2, miny, maxy;
> > +	unsigned long flags;
> > +
> > +	miny = INT_MAX;
> > +	maxy = 0;
> > +
> > +	/*
> > +	 * Merge dirty pages. It is possible that last page cross
> > +	 * over the end of frame buffer row yres. This is taken care of
> > +	 * in synthvid_update function by clamping the y2
> > +	 * value to yres.
> > +	 */
> > +	list_for_each_entry(page, pagelist, lru) {
> > +		start = page->index << PAGE_SHIFT;
> > +		end = start + PAGE_SIZE - 1;
> > +		y1 = start / p->fix.line_length;
> > +		y2 = end / p->fix.line_length;
> > +		if (y2 > p->var.yres)
> > +			y2 = p->var.yres;
> 
> The above test seems contradictory to the comment that
> says the clamping is done in synthvid_update().  Also, since
> the above calculation of y2 is "inclusive", the clamping should
> be done to yres - 1 in order to continue to be inclusive.  Then
> when maxy + 1 is passed to synthvid_update() everything works
> out correctly.
>
[Wei Hu] 
Actually the original code I sent out just works correctly.  It always get
the inclusive rectangle in the above loop, and only send one more extra
line (if y2 == yres) to sythvid_update() and it is clamped inside that 
function. Changing it to yres -1 and sending maxy + 1 to sytnvid_update()
makes it the same as the original code in this case, and would end up 
always copy and refresh one extra row when y2 < yres.

The comment I added was according to your last review comment asking
to add some comments explaining it. Maybe I mis-understood. I thought
since you wanted me to change to maxy + 1, the code could reach yres + 1
so it will be clamped in synthvid_update() to yres.

 Wei


^ permalink raw reply	[flat|nested] 3+ messages in thread

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Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-27 11:25 [PATHC v2] video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver Wei Hu
2019-08-28  0:07 ` Michael Kelley
2019-08-28  9:12   ` Wei Hu

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