RE: [Xen-devel] [PATCH] patch to buffer write ioreq

["Li, Xin B" <xin.b.li@xxxxxxxxx>]

>> This patch implements a new mechanism to buffer the MMIO_WRITE and
>> PIO_WRITE packet in a queue, and then submit them to qemu-dm 
>in batch.
>> This could save a lot of domain switch time. We implement this as a
>> generic one to do ioreq in batch. However, we only use it to 
>batch the
>> MMIO_WIRTE request for stdvga(0xA0000-0xC0000) in order to solve the
>> win2k boot issue for hvm domain.
>> Without this patch, win2k cannot boot up on HVM domain.
>
>Couldn't we just have the VGA area as shared memory, like we do for 
>SVGA? Wouldn't that be faster and simpler?

VGA graphics mode is much more complex than SVGA, since it has several
modes and 4 plane, a pix color is decided by all of the 4 plane, and one
write to 4 plane may happen.
At the beginning, we also have the same idea, but that's not so simple
to implement.

>
>This batched-write mechanism will be redundant when we move to doing 
>all decode and emulation in qemu-dm. (Although I suppose we could keep 
>a really simple decoder in Xen just for certain types of MOV.)

When qemu-dm is moved into minios, we can save a domain switch, so the
batched-write machanism may be not so necessary as today.

-Xin

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