(Another) simple benchmark

Robert Watson rwatson at FreeBSD.org
Sat May 20 17:21:47 UTC 2006

On Fri, 19 May 2006, Ivan Voras wrote:

>> 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.
> Did you miss discussions about how FreeBSD's threading sucks? Ok, "sucks" is 
> maybe a too strong strong word, but if you look for recent discussions about 
> MySQL, you'll see that the difference between Linux and FreeBSD performance 
> is huge.

BTW, there seems to be a fundamental misunderstanding of the benefits of 
threading in the application developer community.  Threading is actually worse 
for performance for a number of application cases.  These tend to be cases 
where the kernel data structures shared across threads are accessed intensely 
across a pool of threads that actually could operate with greater 
independence.  For example, pre-forked web servers vs pre-threaded web 
servers.  If relatively little computation takes place, and it's all a series 
of accept()/send()/sendfile()/close() operations in many threads, you pound 
the locks protecting file descriptor state in the process.  If it were 
different processes, the file descriptor state wouldn't be shared, so 
performance would be greater, even though the context switch cost is greater. 
I've observed this in micro-benchmarks on a number of OS platforms.

Threading is good for application performance where a high level of sharing is 
absolutely necessary -- worker threads working on shared data in a shared 
address space, passing file descriptors between them, lots of synchronization, 
etc.  In many other cases, it's not only not a benefit, but a significant 

Robert N M Watson

More information about the freebsd-performance mailing list