Re: Best combination of workers/CPU cores

Hi,

On Mon, Jul 13, 2009 at 02:47:21PM +0100, Pedro Mata-Mouros Fonseca wrote:
> Greetings,
>
> Other than personally testing it very thouroughly, is there any
> general rule of thumb - regarding HAProxy - as to what combination of
> worker numbers is the most efficient?
>
> I have one HAProxy-only dedicated server with 2 cores and
> Hyperthreading and 3Gb RAM (actually it's two servers, so it's 4
> "cores" per server). Should I have one single worker instance per
> server? Should I have 2? 4? Double of the cores available? Double
> minus one?

You should *always* have "nbproc 1" (the default). It is too much annoying to check stats, logs, control health checks, etc... with multiple processes, and it does not bring a noticeable performance gain at normal levels. In fact, even with only one process, you can make use of multiple cores because the system will be able to run the network cards interrupt drivers on other cores and make use of them. Even on my 10 Gbps machine, I manage to use 3 cores with only one haproxy process, because I have two NICs, each on a different core, and haproxy on a third.

The "nbproc" was implemented to workaround very low file-descriptors limits under Solaris 2.6, and the only solution to have more than 128 concurrent connections was to increase the number of processes.

However, if you can, you should disable hyperthreading on your machine, as experience shows that while it helps with CPU intensive tasks (eg: compilation, video encoding, ...), it hurts with I/O intensive applications (typically network applications). You will then get 2 real cores. Having one process the system and the other run haproxy provides really good results.

Regards,
Willy Received on 2009/07/14 13:32