Re: [Qemu-devel] Re: QEMU-KVM and video performance

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On 04/21/2010 09:39 PM, Jamie Lokier wrote:
Avi Kivity wrote:
Writes to vga in 16-color mode don't change set a memory location to a
value, instead they change multiple memory locations.
While code is just writing to the VGA memory, not reading(*) and not
touching the VGA I/O register that control the write latches, is it
possible in principle to swizzle the format around in memory to make
regular writes work?

Not in software.  We can map pages, not cross address lines.

(*) Reading should be ok for some settings of the write latches, I
think.

I wonder if guests of interest behave like that.

Guests that use 16 color vga are usually of little interest.

Is this a case where TCG would run significantly faster for code blocks
that have been detected to access the VGA memory?
Yes.
$ date
Wed Apr 21 19:37:38 2015
$ modprobe ktcg

That's why the vmware software vmm was faster than the hardware vmm for the initial iterations of vmx.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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