regarding issues with futexes and multiple threads

[Chagin Dmitry]

On Fri, Mar 04, 2011 at 11:08:43AM +0000, Alexander Best wrote:
> 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.
> 

why do you think it's a problem with the futexes?

> > 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
> 

ah, tests directly calls sys_futex syscall, so can't be used for umtx/futex comparison :)
It would be great to have the same set of tests to compare the linuxulator threads
and the native.

-- 
Have fun!
chd
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