Re: [PATCH 1/2] accel/tcg/plugin: export host insn size

[Alex Bennée]

"Wu, Fei" <fei2.wu@intel.com> writes:

> On 4/11/2023 3:27 PM, Alex Bennée wrote:
>> 
>> "Wu, Fei" <fei2.wu@intel.com> writes:
>> 
>>> On 4/10/2023 6:36 PM, Alex Bennée wrote:
>>>>
>>>> Richard Henderson <richard.henderson@linaro.org> writes:
>>>>
>>>>> On 4/6/23 00:46, Alex Bennée wrote:
>>>>>> If your aim is to examine JIT efficiency what is wrong with the current
>>>>>> "info jit" that you can access via the HMP? Also I'm wondering if its
>>>>>> time to remove the #ifdefs from CONFIG_PROFILER because I doubt the
>>>>>> extra data it collects is that expensive.
>>>>>> Richard, what do you think?
>>>>>
>>>>> What is it that you want from CONFIG_PROFILER that you can't get from 
>>>>> perf?
>>>>> I've been tempted to remove CONFIG_PROFILER entirely.
>>>>
>>>> I think perf is pretty good at getting the hot paths in the translator
>>>> and pretty much all of the timer related stuff in CONFIG_PROFILER could
>>>> be dropped. However some of the additional information about TCG ops
>>>> usage and distribution is useful. That said last time I had a tilt at
>>>> this on the back of a GSoC project:
>>>>
>>>>   Subject: [PATCH  v9 00/13] TCG code quality tracking and perf integration
>>>>   Date: Mon,  7 Oct 2019 16:28:26 +0100
>>>>   Message-Id: <20191007152839.30804-1-alex.bennee@linaro.org>
>>>>
>>>> The series ended up moving all the useful bits of CONFIG_PROFILER into
>>>> tb stats which was dynamically controlled on a per TB basis. Now that
>>>> the perf integration stuff was merged maybe there is a simpler series to
>>>> be picked out of the remains?
>>>>
>>>> Fei Wu,
>>>>
>>>> Have you looked at the above series? Is that gathering the sort of
>>>> things you need? Is this all in service of examining the translation
>>>> quality of hot code?
>>>>
>>> Yes, it does have what I want, I suppose this wiki is for the series:
>>>     https://wiki.qemu.org/Features/TCGCodeQuality
>> 
>> Yes.
>> 
>>>
>>> btw, the archive seems broken and cannot show the whole series:
>>>     https://www.mail-archive.com/qemu-devel@nongnu.org/msg650258.html
>> 
>> I have a v10 branch here:
>> 
>>   https://github.com/stsquad/qemu/tree/tcg/tbstats-and-perf-v10
>> 
>> I think the top two patches can be dropped on a re-base as the JIT/perf
>> integration is already merged. It might be a tricky re-base though.
>> Depends on how much churn there has been in the tree since.
>> 
> I have rebased the patches to upstream here:
>     https://github.com/atwufei/qemu/tree/tbstats
>
> I try to keep the patches as possible as they are, but there are lots of
> changes since then, so changes are inevitable, e.g. CF_NOCACHE has been
> removed from upstream, I just removed its usage in the corresponding
> patch, which might not be preferred.

Yeah that fine. CF_NOCACHE was removed to avoid special cases in the
generation code - we simply don't link or store the TBs in the QHT
anymore. As long as the guest isn't executing a lot of non-RAM code we
won't run out of translation buffer too quickly.

>
> I did some basic tests and they worked (the output of info goes to qemu
> console, instead of telnet terminal), including:
>     * tb_stats start
>     * info tb-list
>     * info tb 10
>
> Alex, would you please take a look?

That looks pretty good, glad it wasn't too painful a re-base.

The next question is do you want to pick up the series and put through a
review cycle or two to get merged? It would probably be worth checking
the last posting thread to see if their are any outstanding review
comments.

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro