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

[Alex Bennée]

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 ;-)

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro