Re: [Valgrind-users] RFC: changing Cachegrind default to `--cache-sim=no`

[David F. <fa...@kd...>]

[removing valgrind-developers, since I guess I can't post there]

On lundi 3 avril 2023 11:29:25 CEST Nicholas Nethercote wrote:
> I have been using `--cache-sim=no` almost exclusively for a long time. The
> cache simulation done by Valgrind is an approximation of the memory
> hierarchy of a 2002 AMD Athlon processor. Its accuracy for a modern memory
> hierarchy with three levels of cache, prefetching, non-LRU replacement, and
> who-knows-what-else is likely to be low. If you want to accurately know
> about cache behaviour you'd be much better off using hardware counters via
> `perf` or some other profiler.
> 
> But `--cache-sim=no` is still very useful because instruction execution
> counts are still very useful.
> 
> Therefore, I propose changing the default to `--cache-sim=no`. Does anyone
> have any objections to this?

I agree that simulating a cache from 2002 isn't very useful.

But then, what's the difference between `cachegrind --cache-sim=no`
and `callgrind`?

https://accu.org/journals/overload/20/111/floyd_1886/ says
"The main differences are that Callgrind has more information about the 
callstack whilst cachegrind gives more information about cache hit rates."

Wouldn't one want callstacks? (if this means stack traces).
I know I must be missing something, thanks for enlightening me.

-- 
David Faure, fa...@kd..., http://www.davidfaure.fr
Working on KDE Frameworks 5