[PATCH] D16689: [tsan] Dynamically detect heap range for aarch64.

[Renato Golin via llvm-commits]

rengolin added a comment.

In http://reviews.llvm.org/D16689#359285, @yabinc wrote:

> profiling results on N5X(aarch64) as below:
> mini_bench_local
>  without tsan: 2.50s
>  tsan before: 131s
>  tsan after change: 138s


Ouch!

> According to the results, the performance lose when accessing

>  memory may be about 5%, which seems acceptable.


5% of 5200% is 262% of the initial value!!

I personally don't think that 52x slow down on TSAN is acceptable as it is. This may be AArch64 specific, as I heard from Kostya 2 years ago that it was around 10x for x86_64, but it's definitely not usable.

Thread analysis depends on timing issues too much to make any analysis that runs 52x slower either bogus or very noisy.

This patch is adding a huge list of new instructions to the hot path, and I don't think this will help in any way.

As it happened before multiple times, I think we need to sit down and discuss this issue with kernel and sanitizer engineers. There will be a Linaro Connect in two weeks, and I'll bring that up with the kernel folks this topic, as well as try to reduce the already almost useless slow down.

cheers,
--renato


http://reviews.llvm.org/D16689