What php-fpm settings should I use?

Question

PHP

There is a dedicated production server with the following configuration:
Intel® Core™ i7-920 Quadcore - 4 cores, 48 ​​GB DDR3 RAM, 2 x 2 TB 6 Gb/s SATA 7200 rpm/Enterprise
OS Debian 7
Googled a lot of information, configured php-fpm as recommended online, it looks like this:

pm = dynamic
pm.max_children = 200
pm.start_servers = 12
pm.min_spare_servers = 8
pm.max_spare_servers = 16

Those. I want to allocate 10000 Mb for php for now, taking with a margin the memory usage per process of 50Mb: 10000/50 = 200 max_children. Other parameters are selected from the simplest recommended formulas on the Internet: min_spare_servers = number_cores * 2, max_spare_servers = number_cores * 4, and start_servers = min_spare_servers + (max_spare_servers - min_spare_servers) / 2.
But one fig in the error logs:

WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 7 idle, and 29 total children
WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 7 idle, and 28 total children
WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min /max_spare_servers), spawning 8 children, there are 6 idle, and 55 total children
WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 7 idle, and 64 total children

So how to correctly calculate and set these parameters?

Answer 1

It's decided. The brakes were caused by sending mail and hanging scripts for several minutes.

Answer 2

Maybe it's time to look towards HHVM?) If the code is adequately written, then there shouldn't be any big difficulties.