[PATCH] D16689: [tsan] Dynamically detect heap range for aarch64.
Renato Golin via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 23 01:29:21 PST 2016
rengolin added a comment.
In http://reviews.llvm.org/D16689#359285, @yabinc wrote:
> profiling results on N5X(aarch64) as below:
> without tsan: 2.50s
> tsan before: 131s
> tsan after change: 138s
> 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.
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