Re: [Performance of circular_buffer vs Queue][Multithreading may be broken]

From: Jan Hafer (jan.hafer_at_[hidden])
Date: 2020-04-02 19:41:15

On 02.04.20 20:59, Mathias Gaunard wrote:
> On Thu, 2 Apr 2020 at 17:43, Jan Hafer via Boost <boost_at_[hidden]> wrote:
> 
> 
>> Yes, I do use 1 buffer/queue per thread.
> 
> So you're saying that circular_buffer is slower on a given thread when
> other threads are accessing their own circular_buffer in parallel?
> That sounds unlikely to be circular buffer's fault.

Yes and I dont know quite the reason for it.
My Threads know their id to access a file-global data structure
containing their queue/circular buffer. They start another after in a
thread-safe way and exit on emptying the queue/circular buffer.

> 
> The first thing to check is that the memory placement of your circular
> buffer does not result in false sharing with other threads.
> More generally you could be stalling due to any inter-connection, such
> as crossing NUMA domains or talking to hardware.
> Otherwise you could be saturating the execution ports of your core and
> thus not get the expected speed-up from hyper-threading, but in any
> case you'd be the best throughput overall.
> 

I know how to obtain the source code of boost, but the compiler vendors
sadly provide no direct internet-searchable links to the std source code.
Thanks for your advice. I may dig further with perf to obtain cache-miss
statistics.

My goal was just to inform you of this characteristics, since this is
not documented.