[LLVMdev] multithreaded performance disaster with -fprofile-instr-generate (contention on profile counters)

[Duncan P. N. Exon Smith]

(Sorry to jump in before reading the whole thread...)

On 2014-Apr-24, at 1:33, Dmitry Vyukov <dvyukov at google.com> wrote:

> On Wed, Apr 23, 2014 at 10:48 PM, Bob Wilson <bob.wilson at apple.com> wrote:
>> I can see that the behavior of our current instrumentation is going to be a
>> problem for the kinds of applications that you’re looking at. If you can
>> find a way to get the overhead down without losing accuracy
> 
> What are your requirements for accuracy?
> Current implementation does not provide 100% accuracy, so it's
> something less than 100%. 

Modulo any bugs, my understanding is that the current implementation
*does* provide 100% accuracy for single-threaded applications, as long
as the counters don't overflow.  Am I missing something?