Interesting that the linux you are claiming to use would use prefork
Apache as default, while this is the default on FreeBSD I would think
the threaded worker would be used on a lot of linux dists, since they
don't have the option to easily rebuild it.
Even if it is using prefork, the Linux Apache conf prefork settings
already are set higher, the start up server is 8 and has a higher max
spare server setting of 20 (double the setting of default FreeBSD
setting), I have found that ab is a kind of weird program and initial
settings of the Apache server (its ability to initially respond) do
adversely affect its ability to do the ab benchmark for some reason.
Considering you are trying to initiate 100 connections at the same time
with a prefork server that even one the better configured Linux side
(with 8 initial servers which would quickly jump to 13) its not a very
valid benchmark setup, especially with the unforgiving ab benchmark tool
Something else you should look at when using Apache on FreeBSD is the
Apache accept kernel module to save context switches which is aimed at
increasing performance.
man accf_http
Sometimes I look at the ab program as something that better shows off
the abilities of the Zeus server considering that the ab benchmark tool
doesn't have some sane benchmark options such as constant connection
rate modes unlike programs like 'httperf' do (which is in the ports tree)
Such simple settings such as prefork might work fine for people running
a simple CGI site or a PHP site (if there not going to load zend
performance modules or use the encoder), if you have done benchmarks on
PHP its surprisingly slow technology, on top of the fact that PHP folk
recommend nothing other then prefork mode with PHP.
If I was working on a project such as Apache I know I wouldn't be
concentrating of performance with prefork in this day when threaded
modes are where Apache has been aiming for modern high performance web
serving for a fair while now.
Mike
Ivan Voras wrote:
Sorry, I forgot about performance@ mailing list, moving the discussion
there - please use performance at freebsd.org or equivalent address
when replying (and drop current@).
Steve Hodgson wrote:
Ivan Voras wrote:
Today I had the opportunity to experiment for a short time with a
4-CPU Xeon machine with hyperthreading (-> 8 logical CPU-s) and 3GB
RAM. In absence of anything smarter to do, I installed WBEL 3 Linux
(non-RedHat version of RedHat Enterprise Linux) which was accidentally
on the table and after toying around I've run a simple benchmark - ab
(apachebench, included by default with apache server) over localhost
to a local apache2 server, on a static home-page file. The command
line was "ab -n 100000 -c 100 http://localhost/";. Since I still had
time with the machine, I then downloaded and installed FreeBSD 6.1 to
try to beat the score. Unfortunately, not only I couldn't beat the
score, but the results were *extremely* bad. Since I'm still not sure
it isn't my fault, I won't post the actual results, but I wonder...
Apache is a well known server-grade product, which doesn't use
threading (it was preforked in both systems), doesn't call
gettimeofday() constantly, uses sendfile(), and in short, is very
different from MySQL. It shouldn't behave this badly on FreeBSD.
Some observations from the benchmark runs:
- Linux was maxed out with ~50% total idle time, each logical
processor (hyperthreading was enabled) had ~25% user + ~25% sys time.
It still delivered order-of-magnitude better results. WBEL3 uses Linux
2.4.x kernel (i.e. old kernel)
- FreeBSD CPU time was 100% spent, with 90%-95% spent in sys time
- On FreeBSD, enabling hyperthreading got me a slowdown of *4x* over
the initial (bad) results (some slowdown is not surprising, 4x
slowdown is).
- Linux "load average" never went above 8, FreBSD's went > 60; this
could be just a difference in accounting, or it could not - I don't
know.
What is needed to reproduce this simple benchmark:
- SMP machine, the more CPUs the better
- installed software: only apache20. The "ab" benchmark is included in
it. Leave apache's default configuration as-is (i.e. preforked, max
150 parallel clients allowed)
- A simple static HTML page (Apache's default "welcome, but this site
is not configured" should be ok).
- my invocation of "ab" was with "-n 100000 -c 100" ; the (n)umber of
requests could be modified to fit local CPU speed, but (c)oncurrency
shouldn't (100 parallel requests is not uncommon).
Apache may not use gettimeofday, but ab certainly does. here is a truss
output of ab:...
I don't think this would result in 90% time being spent in sys with
large load averages.
A fairer test would be to use ab on a second box and keep ab on the same
OS - you're changing two things at once here. You're also at the mercy
of how the scheduler places the processes across the different CPU's
(since there is one ab process and multiple httpd processes). Why was
Linux stuck at 50% utilization per CPU (surely it should reach 100% with
no disk or network constraints)? Perhaps it is sleeping whilst FreeBSD
spins?
If you are interested in performance try Lighttpd - that is what people
use if they want high transaction rates (x10 higher in tests I've done
on Linux) - and it is a single process so scheduling isn't so
significant.
Using lighttpd or ab on other host is not really applicable - I wasn't
trying to configure the box for production, only ran the benchmarks
out of curiosity. Apache *should* work ok out of the box on FreeBSD :)
(btw. apache was installed from binary package)
Here are the apache config files:
http://ivoras.sharanet.org/stuff/httpd.conf.tbz
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