Re: [REPORT] [GSoC - TCG Continuous Benchmarking] [#2] Dissecting QEMU Into Three Main Parts

[Alex Bennée]

Aleksandar Markovic <aleksandar.qemu.devel@gmail.com> writes:

> On Wednesday, July 1, 2020, Alex Bennée <alex.bennee@linaro.org> wrote:
>
>>
>> Ahmed Karaman <ahmedkhaledkaraman@gmail.com> writes:
>>
>> > On Mon, Jun 29, 2020 at 6:03 PM Alex Bennée <alex.bennee@linaro.org>
>> wrote:
>> >>
>> >> Assuming your test case is constant execution (i.e. runs the same each
>> >> time) you could run in through a plugins build to extract the number of
>> >> guest instructions, e.g.:
>> >>
>> >>   ./aarch64-linux-user/qemu-aarch64 -plugin tests/plugin/libinsn.so -d
>> plugin ./tests/tcg/aarch64-linux-user/sha1
>> >>   SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
>> >>   insns: 158603512
>> >>
>> >> --
>> >> Alex Bennée
>> >
>> > Hi Mr. Alex,
>> > I've created a plugins build as you've said using "--enable-plugins"
>> option.
>> > I've searched for "libinsn.so" plugin that you've mentioned in your
>> > command but it isn't in that path.
>>
>> make plugins
>>
>> and you should find them in tests/plugins/
>>
>>
> Hi, both Alex and Ahmed,
>
> Ahmed showed me tonight the first results with number of guest
> instructions. It was almost eye-opening to me. The thing is, by now, I had
> only vague picture that, on average, "many" host instructions are generated
> per one guest instruction. Now, I could see exact ratio for each target,
> for a particular example.
>
> A question for Alex:
>
> - What would be the application of this new info? (Except that one has nice
> feeling, like I do, of knowing the exact ratio host/guest instruction for a
> particular scenario.)

Well I think the total number of guest instructions is important because
some architectures are more efficient than others and this will an
impact on the total executed instructions.

> I just have a feeling there is more significance of this new data that I
> currently see. Could it be that it can be used in analysis of performance?
> Or measuring quality of emulation (TCG operation)? But how exactly? What
> conclusion could potentially be derived from knowing number of guest
> instructions?

Knowing the ratio (especially as it changes between workloads) means you
can better pin point where the inefficiencies lie. You don't want to
spend your time chasing down an inefficiency that is down to the guest
compiler ;-) 

>
> Sorry for a "stupid" question.
>
> Aleksandar
>
>
>
>
>> >
>> > Are there any other options that I should configure my build with?
>> > Thanks in advance.
>> >
>> > Regards,
>> > Ahmed Karaman
>>
>>
>> --
>> Alex Bennée
>>


-- 
Alex Bennée