Displaying 2 results from an estimated 2 matches for "400bab".
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2014 Apr 18
4
[LLVMdev] multithreaded performance disaster with -fprofile-instr-generate (contention on profile counters)
On Fri, Apr 18, 2014 at 12:13 AM, Dmitry Vyukov <dvyukov at google.com> wrote:
> Hi,
>
> This is long thread, so I will combine several comments into single email.
>
>
> >> - 8-bit per-thread counters, dumping into central counters on overflow.
> >The overflow will happen very quickly with 8bit counter.
>
> Yes, but it reduces contention by 256x (a thread
2014 Apr 23
4
[LLVMdev] multithreaded performance disaster with -fprofile-instr-generate (contention on profile counters)
...b97: 48 ff 05 42 25 20 00 incq 0x202542(%rip) # 6030e0 <__llvm_profile_counters__ZNSt6vectorIiSaIiEEixEm>
> 400b9e: 48 8b 05 4b 26 20 00 mov 0x20264b(%rip),%rax # 6031f0 <v>
> 400ba5: c7 00 2a 00 00 00 movl $0x2a,(%rax)
> 400bab: c3 retq
>
> Suddenly, an innocent function that uses std::vector becomes a terrible point of contention.
> Full test case below, -fprofile-instr-generate leads to 10x slowdown.
>
> =========================
>
> Now, here is a more detailed pro...