Re: [Boost-users] Boost interprocess containers - performance issue

Subject: Re: [Boost-users] Boost interprocess containers - performance issue
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2012-03-11 07:21:36

El 11/03/2012 1:00, Naveen Santhapuri escribió:
> Hello all,
>
>       I am experimenting with Boost interprocess containers and like the
> ease of using them. I want to use these in place of the "linux shared
> memory+shared memory allocator + std containers". However, I am seeing
> some performance hit when using boost. I measured the times for vector
> access from shared memory. I define access as indexing into the vector
> (v[i]) (all times in milli seconds):
>
>      Num elements   Local heap | Boost ipc | Shmat()
>         100,000            0.23           0.39             0.27
>      1,000,000             2.3            3.85             2.7

What does Shmat mean? Are you putting a std::vector directly in a shared 
memory segment?

Obviously if you put boost containers in shared memory you don't store 
raw pointers (as every process can map the memory in a different 
address, making raw pointers unusable). When using offset_ptr we have a 
performance hit as we need to calculate the real address computing a 
pointer arithmetic (this + stored offset). Apart from that, as 
offset_ptr relies on undefined behaviour, the offset calculation must be 
marked as non-inlineable in most compilers, increasing the performance 
hit. I think it can be improved using some kind of compiler-specific 
annotations or assembler, but I have no skills to do that nowadays.

Best,

Ion