Thread performance (was Re: dynamic context transitions)

[David Collier-Brown]

On Wed, Dec 01, 2004 at 05:12:24PM -0600, Christopher R. Hertel wrote:
>>I've been asking about this in different places.  I've heard theories, 
>> mostly.  This is happening in Linux (dunno if it's been tested elsewhere) 
>> and one theory is that the forked process speeds are good because Linux 
>> basically does a really good job with those.  Meanwhile, thread speed is 
>> bad because the multiple threads are all within a single process and the 
>> single process gets only it's own share of processor time.

	That was the case with Solaris 7: it was changed to
	one kernel thread per user thread in 8, vaguely similar
	to the Linux one process-equivalent per thread.

Russell Coker <russell at coker.com.au> wrote:
| Probably threads are best restricted to languages such as Java and Ada 

	Threads aren't even second-class objects in C: as a result
	they're surprisingly hard to debug and maintain. (Languages
	where "classes and monitors" are first-class objects have far
	less difficulty dealing with them.)

	From Tridge's comment, it appears then Linux libc2 tries to make
	threads behave like first-class objects, with locking around
	thread-unsafe interfaces, for a gain is correctness and a loss in speed.

	The Solaris model is to assume programs are unthreaded, and 
	make it the programmer's responsibility to chose the thread-safe
	and high-threaded-performance interfaces, and no others. There
	are no locks or warnings about using a thread-unsafe libc function,
	it just fails at runtime.

	Expect a threaded program that runs correctly in Linux to fail 
	randomly and mysteriously in Solaris, HP/UX and the like...

	This makes it startlingly hard to do portable threaded programs (:-))

--dave (engaging in positively British understatement) c-b
-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain