Re: [PATCH v2 28/30] KVM: x86 emulator: restart string instruction without going back to a guest.

[Avi Kivity <avi@redhat.com>]

On 03/15/2010 12:19 PM, Gleb Natapov wrote:
> On Mon, Mar 15, 2010 at 12:15:22PM +0200, Avi Kivity wrote:
>    
>> On 03/15/2010 12:07 PM, Gleb Natapov wrote:
>>      
>>>        
>>>> Or we can make the buffer larger for everyone (outside this patchset
>>>> though).
>>>>
>>>>          
>>> I am not sure what do you mean here. INS read ahead and MMIO read cache are
>>> different beasts. Former is needed to speed-up string pio reads, later
>>> (not yet implemented) is needed to reread previous MMIO read results in
>>> case instruction emulation is restarted due to need to exit to userspace.
>>> MMIO read cache need to be invalidated on each iteration of string
>>> instruction.
>>>        
>> Instructions with multiple reads or writes need an mmio read/write
>> buffer that can be replayed on re-execution.
>>
>> buffer != cache!  A cache can be dropped (perhaps after flushing it
>> to a backing store), but a buffer in general cannot.
>>
>>      
> That is just naming. Call it "buffer" if you want.
>
> I still don't understand what do you mean by "Or we can make the buffer
> larger for everyone". Who is this "everyone"? Different instruction need
> different kind of buffers.
>    

Many instructions can issue multiple reads, ins is just one of them.  A 
generic mmio buffer can be used by everyone.

-- 
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