regarding issues with futexes and multiple threads

Alexander Best arundel at freebsd.org
Fri Mar 4 11:08:43 UTC 2011


On Fri Mar  4 11, Chagin Dmitry wrote:
> On Thu, Mar 03, 2011 at 09:20:51PM +0000, Alexander Best wrote:
> > hi there,
> > 
> > i've been investigating this issue for quite a while now and simply wanted to
> > post some measurements i did.
> > 
> > basically there's a massive slowdown when a process triggers a lot of threads
> > which are doing futex operations. the following example is from darren hart's
> > futex test suite (performance/). the slowdown seems to SMP related. here are
> > the measurements running with SMP enabled and with kern.smp.disabled=1:
> > 
> 
> 1) slowdown is expected behaviour.

even if the slowdown is to be expected, looking at the screenshot with the
top(1) output it seems obvious that there are issues with the current futex
implementation.

> 2) is it possible to run this test suite on FreeBSD?

i used emulators/linux_dist-gentoo-stage3 to compile the testsuite and then ran
it natively under freebsd. if you want to i can send you the file. it's

futex_wait: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped

cheers.
alex

ps: there should be a link to the futex testsuite on the freebsd linuxulator
wiki.

> 
> --
> chd,
> Have fun!
> 



-- 
a13x


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