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Re: [Qemu-discuss] Guest execution statistics from QEMU

From: Jakob Bohm
Subject: Re: [Qemu-discuss] Guest execution statistics from QEMU
Date: Mon, 18 Aug 2014 14:50:43 +0200
User-agent: Mozilla/5.0 (Windows NT 5.2; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.0

On 8/18/2014 2:26 PM, Mie Ite wrote:
Hi everyone,

I would like to know the following information of the guest application 
executed in QEMU:

- the number of guest instructions executed per each function call
- the number of memory access instructions
- the address and size of each executed load / store

It it possible to extract any of the above from stock QEMU currently or should 
I start to look at the source code?

Probably not.  Qemu (like most other virtual machine engines) are
trying to run the guest code as fast as possible without letting it
touch the host system, so counting individual instructions would be
unwanted overhead.  Also, to qemu, the function calls in the guest
application don't really exist, only the various instructions, some
of which happen to implement the function call mechanism of a higher
level language.

Also these particular statistics are so rarely wanted for modern CPU
architectures, where the execution "cost" (time, energy) of individual
instructions is highly variable due to hardware features such as
superscalar execution, pipelining, microcode, caching etc.

All that said, I don't know if the TCG emulator in qemu (its slowest
mode) can be easily configured or patched to collect some statistics
about each emulated instruction.


Jakob Bohm, CIO, Partner, WiseMo A/S.  http://www.wisemo.com
Transformervej 29, 2730 Herlev, Denmark.  Direct +45 31 13 16 10
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