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

[Philippe Mathieu-Daudé]

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.

> + * This plugin can be used to restrict the execution of a system to a
> + * particular number of Instructions Per Second (ips). This controls
> + * time as seen by the guest so while wall-clock time may be longer
> + * from the guests point of view time will pass at the normal rate.
> + *
> + * This uses the new plugin API which allows the plugin to control
> + * system time.
> + *
> + * Copyright (c) 2023 Linaro Ltd
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */