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[Xen-devel] Re: [PATCH][HVM] remove qemu shadow_vram patch for performan

To: Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH][HVM] remove qemu shadow_vram patch for performance
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Wed, 21 Mar 2007 16:09:25 -0500
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
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Keir Fraser wrote:

On 15/3/07 03:30, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:

remove qemu shadow_vram patch and force a whole screen update each time for

W/O this patch, there is huge performance drop in HVM domain when adding other
guest(windows or linux with xwindow).

shadow_vram_revert.patch - revert the shadow_vram patch
shadow_vram_force_update.patch - explictly redraw screen each time

How can updating the whole screen 30 times a second be faster than the
memcmp() that we do currently?

It really depends. The VNC display already has a minimization mechanism so doign the memcmp() in the vga driver doesn't help at all.

For SDL, when using X, it's going to be doing an XShmImage so the difference is only in the size of update (no data is transferred to the X server). If the X server is double buffering the framebuffer (which I have to assume it's doing), then you're just paying the cost of a memcpy() in the X server that you would normally pay in qemu-dm.

However, if you're forwarding SDL over X, or for some reason your X server isn't using XShmImage, this patch will slow things down considerably.

Perhaps this should be made a configuration option?


Anthony Liguori

 -- Keir

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