Re: #15646 BerkeleyDB hybrid mutexes

[Howard Chu <hyc@symas.com>]

Keith Bostic wrote:
> On Oct 9, 2007, at 12:02 AM, Howard Chu wrote:
>
> > With a CPU-hog running in the background, the test with BDB 4.2.52
> > takes only 37 seconds, while BDB 4.6.21 takes 1:42. Watching with
> > top you can see that BDB 4.6.21 gets a lot less CPU than BDB
> > 4.2.52. This is the problem with using yield() on an NPTL system -
> > whereas on most POSIX systems yield() only yields control to some
> > other thread in the current process, on NPTL yield() gives up the
> > CPU for the entire process.
>
> Is there a call that would be preferable on NPTL?
>
> What call on NPTL will only yield control from the thread, not the
> entire process?

When we first encountered this problem in the OpenLDAP source we used select() 
with a zero timeout. But I recall that that performed poorly as well, and 
nowadays we just avoid doing any type of yield at all. I think the real answer 
here is that on Linux 2.6 you really just want to use the native mutex 
(pthread, futex, whatever it's called) and not do anything else.

--
  -- Howard Chu
  Chief Architect, Symas Corp.  http://www.symas.com
  Director, Highland Sun        http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP     http://www.openldap.org/project/