Re: [PATCH 9/9] contrib/plugins: add ips plugin example for cost modeling

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 6/16/24 11:43, Alex Bennée wrote:
> Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:
> 
>> On 6/13/24 01:54, Philippe Mathieu-Daudé wrote:
>>> On 12/6/24 17:35, Alex Bennée wrote:
>>>> From: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>>>>
>>>> This plugin uses the new time control interface to make decisions
>>>> about the state of time during the emulation. The algorithm is
>>>> currently very simple. The user specifies an ips rate which applies
>>> ... IPS rate (Instructions Per Second) which ...
>>>
>>>> per core. If the core runs ahead of its allocated execution time the
>>>> plugin sleeps for a bit to let real time catch up. Either way time is
>>>> updated for the emulation as a function of total executed instructions
>>>> with some adjustments for cores that idle.
>>>>
>>>> Examples
>>>> --------
>>>>
>>>> Slow down execution of /bin/true:
>>>> $ num_insn=$(./build/qemu-x86_64 -plugin ./build/tests/plugin/libinsn.so -d plugin /bin/true |& grep total | sed -e 's/.*: //')
>>>> $ time ./build/qemu-x86_64 -plugin ./build/contrib/plugins/libips.so,ips=$(($num_insn/4)) /bin/true
>>>> real 4.000s
>>>>
>>>> Boot a Linux kernel simulating a 250MHz cpu:
>>>> $ /build/qemu-system-x86_64 -kernel /boot/vmlinuz-6.1.0-21-amd64 -append "console=ttyS0" -plugin ./build/contrib/plugins/libips.so,ips=$((250*1000*1000)) -smp 1 -m 512
>>>> check time until kernel panic on serial0
>>>>
>>>> Tested in system mode by booting a full debian system, and using:
>>>> $ sysbench cpu run
>>>> Performance decrease linearly with the given number of ips.
>>>>
>>>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>>>> Message-Id: <20240530220610.1245424-7-pierrick.bouvier@linaro.org>
>>>> ---
>>>>     contrib/plugins/ips.c    | 164 +++++++++++++++++++++++++++++++++++++++
>>>>     contrib/plugins/Makefile |   1 +
>>>>     2 files changed, 165 insertions(+)
>>>>     create mode 100644 contrib/plugins/ips.c
>>>>
>>>> diff --git a/contrib/plugins/ips.c b/contrib/plugins/ips.c
>>>> new file mode 100644
>>>> index 0000000000..db77729264
>>>> --- /dev/null
>>>> +++ b/contrib/plugins/ips.c
>>>> @@ -0,0 +1,164 @@
>>>> +/*
>>>> + * ips rate limiting plugin.
>>> The plugin names are really to packed to my taste (each time I look
>>> for
>>> one I have to open most source files to figure out the correct one); so
>>> please ease my life by using a more descriptive header at least:
>>>         Instructions Per Second (IPS) rate limiting plugin.
>>> Thanks.
>>>
>>
>> I agree most of the plugin names are pretty cryptic, and they are
>> lacking a common "help" system, to describe what they do, and which
>> options are available for them. It's definitely something we could add
>> in the future.
>>
>> Regarding what you reported, I'm totally ok with the change.
>>
>> However, since this is a new series, I'm not if I or Alex should
>> change it. If it's ok for you to modify this Alex, it could be simpler
>> than waiting for me to push a new patch with just this.
> 
> Its my tree so I'll fix it up. I'll ask you if I want a respin ;-)
> 

Thanks Alex.