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Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman
From: |
Stefano Stabellini |
Subject: |
Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman |
Date: |
Thu, 20 Sep 2012 12:33:32 +0100 |
User-agent: |
Alpine 2.02 (DEB 1266 2009-07-14) |
On Thu, 20 Sep 2012, Gerd Hoffmann wrote:
> > Pixman or non-pixman, I still think that this could benefit from
> > implementing a DisplayAllocator interface: it would avoid a memcpy
> > whenever there is no need for scaling and pixel conversions.
>
> There is one more issue I didn't mention yet: The framebuffer memory
> should better be treaded as write-only memory as this is what gfx cards
> are optimized for. Read access works of course, but can be _very_ slow
> depending on the hardware.
That is true, however do we actually read the framebuffer back anywhere?
I don't think that the vga emulator reads back anything.
In any case if the memory is WC, there might still be some benefit in
writing the framebuffer all in one go but I don't think that the
difference would noticeble. If it is, it might be a good idea to get rid
of DisplayAllocator altogether.
> So implementing a DisplayAllocator and thereby making the vga emulation
> operate directly on framebuffer memory is a very bad idea IMO. Most
> likely it will make certain operations (like cirrus bitblits) slower
> even though it saves a memcpy.
It is not just one memcpy less, it is also about zero latency.
Otherwise we have the typical problem of having to wait 30ms before the
screen update. Not nice.
- [Qemu-devel] [PATCH 5/9] fbdev: add monitor command to enable/disable, (continued)
- [Qemu-devel] [PATCH 5/9] fbdev: add monitor command to enable/disable, Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 6/9] fbdev: make configurable at compile time., Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 2/9] add unregister_displaychangelistener, Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 9/9] fbdev: add display scaling support, Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 3/9] move set_mouse + cursor_define callbacks, Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 8/9] fbdev: add mouse pointer support, Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 1/9] QLIST-ify display change listeners., Gerd Hoffmann, 2012/09/19
- [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Gerd Hoffmann, 2012/09/19
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Stefano Stabellini, 2012/09/19
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Gerd Hoffmann, 2012/09/20
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman,
Stefano Stabellini <=
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Gerd Hoffmann, 2012/09/20
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Stefano Stabellini, 2012/09/20
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Gerd Hoffmann, 2012/09/20
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Stefano Stabellini, 2012/09/20
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Stefano Stabellini, 2012/09/20
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Gerd Hoffmann, 2012/09/21
- Re: [Qemu-devel] [PATCH 7/9] fbdev: move to pixman, Stefano Stabellini, 2012/09/21
[Qemu-devel] [PATCH 4/9] fbdev: add linux framebuffer display driver., Gerd Hoffmann, 2012/09/19