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

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

>> When we boot win2k guests, just after windows enters standard VGA
>> graphics mode, it keeps updating a flashing bar to indicate it's in
>> booting process, but seems this screen updating in win2k guest is
>> executed as a very high priority task, so win2k can not boot.
>> The phenomenon is, If in 10ms, about 600 standard VGA MMIO writes can
>> happen, win2k can boot normally. If less or about 500 writes 
>happen, it
>> can _not_ boot and just keeps updating the flashing bar, we 
>ever waited
>> for several hours to see if it can boot, but the guest made no more
>> progress. I guess there is a threshold for win2k to boot.
>
>That's quite amusing! Of course, even with batching the machine may be 
>slow or loaded enough to cause problems...

You're definitely right, on some slow machine, we watched this :-(.


>
>I wonder if putting the VGA emulation in Xen itself would make sense? 
>The 'backend protocol' is just a simple linear framebuffer after all: 
>nothing very complicated (much simpler and easier to put in Xen than 
>xenbus/blk/net). VGA MMIO access would then be about as "fast" as a 
>vmenter/vmexit roundtrip. The main downside is that it might 
>limit what 
>tricks we can do with the backend video protocol in future.

Maybe it's worth to have a try :-)
-Xin


>
>  -- Keir
>
>
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