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

["Zhai, Edwin" <edwin.zhai@xxxxxxxxx>]

On Thu, Mar 15, 2007 at 10:50:13AM +0000, 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
> > performance.
> > 
> > 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?

as far as i can tell, the bottle neck is that orig method does memcmp and 
memcpy 
byte by byte. furthermore, orig method can void a update by multiple memcmp 
only 
if all bytes are equal, which is in the minority.

there is no doubt we need a vram dirty for qemu, but current one is not the 
best. we can make a new one in future by shadow or something else.

thanks,

> 
>  -- Keir
> 

-- 
best rgds,
edwin

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