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

[Aleksandar Markovic]

On Saturday, July 4, 2020, Alex Bennée <alex.bennee@linaro.org> wrote:
> 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 ;-)

Yes, it is definitely worth having the exact number of guest instructions!

Ahmed and I knew from the outset, like everybody else for that matter, that workload and guest compiler and architecture itself immensly impact any measurement.

However, if we keep the same guest, guest compiler, and workload as well, and change just qemu, than we should be able to draw conclusion on qemu-specific issues, and hopefully remove some inefficiencies. I hope you will see that approach in next Ahmed's reports.

Aleksandar

 

> >
> > 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