Number of worker processes on hyperthreaded processor

Jérémy Lecour jeremy.lecour at
Sat Jan 19 22:57:48 UTC 2013

2012/11/19 Eric Wong <normalperson at>:
> Andrew Stewart <boss at> wrote:
>> Good morning,
>> The tuning page says worker_processes should be at least the number of
>> CPU cores on a dedicated server.  In the case of hyper-threading,
>> should this be the number of cores or the number of threads?
>> For example the Intel Core i7-2600 Quadcore[1] has 4 cores and 8
>> threads.  Would I start my worker_processes at 4 or 8?
> I'd start with the number of threads, since (AFAIK) your CPU implements
> HT well (unlike the P4 family).  Modern OSes multitask well, so more
> worker processes will always work until it bumps into another limit
> (e.g. memory usage, DB connections, disk contention, ...)

Hi (in plain text this time, sorry),

I have a follow up question about this.

What about having a few different unicorns (1 for each Ruby/Rails app)
on a singe server ; "at least the number of CPU cores" should count
the total number of children processes, or only per app ?

To be extremely clear ; if I have 2 quad-core CPUS with HT (eg. 16
cores), can I have 16 unicorn workers per app, or total ?


PS : I've had my first unicorns in production for a few days, and I'm
very happy about this wonderful piece of software. Thanks for
making/maintaining it.

Jérémy Lecour : -

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