Re: [Qemu-devel] [PATCH v2 5/6] vga: Use linear mapping + dirty logging in chain 4 memory access mode

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-08-19 08:19, Avi Kivity wrote:
> On 08/18/2011 03:26 PM, Jan Kiszka wrote:
>> On 2011-08-17 16:48, Avi Kivity wrote:
>> >  On 08/17/2011 04:38 PM, Avi Kivity wrote:
>> >>
>> >>  The mmio code has
>> >>
>> >>              s->plane_updated |= mask; /* only used to detect font
>> >>  change */
>> >>
>> >>  aren't we losing it?  we could easily recover it via dirty logging.
>> >>
>>
>> Yes, I forgot to forward-port plane_updated = 0xf from v1 of the patch.
>>
>> >
>> >  We can't really recover it.
>>
>> I don't see yet why we should not if we simply enforce a full update.
>> Can you elaborate?
> 
> If we go for a full update we might as well disable dirty logging entirely.

Full update only affects text screen refreshes. The guest access to the
VRAM will still benefit from the much faster mmio.

> 
>>
>> >   So I think we need to restrict the
>> >  optimization to graphic mode.
>> >
>> >  Is grub using text mode or graphic mode?
>> >
>> >  If it's using text mode, it may be faster to compare the font plane
>> to a
>> >  snapshot from the last redraw than to take an exit.
>>
>> I wasn't optimizing for text mode here, it's just a side effect if it
>> happens to benefit from it as well. I could exclude it, but only if
>> really needed.
>>
> 
> Ok, so grub is using graphic mode?

Yep.

> 
> 
> We'll need to force full updates in text mode then.

Right. I'll sent an update doing that. There are some other quirks of
the series remaining I'm addressing ATM.

Jan


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