Re: [Qemu-devel] How to measure guest memory access (qemu_ld/qemu_st) time?

[Blue Swirl]

On Mon, Jun 18, 2012 at 4:59 AM, YeongKyoon Lee
<address@hidden> wrote:
>> The idea looks nice, but instead of different TLB functions selected
>> at configure time, the optimization should be enabled by default.
>>
>> Maybe a 'call' instruction could be used to jump to the slow path,
>> that way the slow path could be shared.
>
> I had considered the approach of sharing slow path, actually argument 
> settings for ld/st helper functions.
> However, the problem is that we don't know which runtime registers having 
> arguments.

Hm, I didn't consider that.

>
> There are three possible solutions for sharing, I think.
> 1. Using code stub table including all the possible argument register 
> combinations
> 2. Using register information flag constant generated at TCG time, and a 
> special stub which parsing the flag and setting the arguments
> 3. Setting the arguments commonly for fast and slow paths, which needs 
> additional stack or register cleanup for fast path
>
> I think the solution #2 looks better for performance, however, it could be 
> implemented using jump and assembly because using call could come together 
> with unwanted code and register clobber by the prolog of callee.
> But it might be painful of implementing the parsing stub using assembly (or 
> code generation). It is the weak point of solution #2.
>
> How do you think about it?

I agree that #2 looks best.

>
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