Re: What riscv tracing tools do you recommend and how are they accurate for measurements?

[Alistair Francis]

On Thu, Feb 29, 2024 at 11:21 PM Nazerke Turtayeva <nturtayeva@ucsb.edu> wrote:
>
> Hi everyone,
>
> Recently, I was planning to measure the performance of my application of 
> interest for potential RISC-V hardware. Hence, I started my simulations from 
> Spike to analyze dynamic instruction traces and instruction count, 
> nevertheless given it does not support multithreading, I started using Qemu 
> to test my app too. However, it seems like I cannot rely on timing results of 
> Qemu for comparing different implementations. Accordingly, given I am brand 
> new to the Qemu ecosystem, I was wondering whether I am missing some 
> important mainstream instrumentation and tracing tools that I can use for 
> performance evaluation of my target app in other ways. Particularly, I want 
> to understand implications of adding custom ISA instructions to the 
> performance of my application.

Hello,

QEMU is an emulator so it isn't great at timing analysis.

QEMU is useful for instruction traces though. If you use icount [1]
you can get a deterministic-ish setup which is very useful for
instruction counting during execution. I'm not sure what custom
instructions you are adding, but you can test if they reduce the
number of instructions executed. Note that QEMU doesn't model timing
though, so it might not be an accurate representation of real life
performance.

You can use a plugin (see [2] for some examples) to generate
instruction, memory or other more specific traces.

1: https://www.qemu.org/docs/master/devel/tcg-icount.html
2: https://www.qemu.org/docs/master/devel/tcg-plugins.html#example-plugins

Alistair

>
> In this regard, do you have any recommendations on where I can look?
>
> Thanks,
> Best wishes
>
> --
> Nazerke Turtayeva
> Graduate Student
> Electrical and Computer Engineering, Computer Science
> Email: nturtayeva@ucsb.edu
> UC Santa Barbara