Re: [boost] Boost.Atomic, pushing forward and a little request for help

Subject: Re: [boost] Boost.Atomic, pushing forward and a little request for help
From: Helge Bahmann (hcb_at_[hidden])
Date: 2011-08-07 14:41:16

On Saturday 06 August 2011 07:40:02 Gottlob Frege wrote:
> On Wed, Aug 3, 2011 at 11:52 AM, Phil Endecott
>
> <spam_from_boost_dev_at_[hidden]> wrote:
> > Helge Bahmann wrote:
> >> On Tuesday 02 August 2011 19:28:08 Phil Endecott wrote:
> >>> The thing that I believe is missing is tests.  Do you have any thoughts
> >>> about that?
> >>
> >> Well, I have a few simple tests for atomicity only, they are hand-built
> >> and I am working to push them into the boost build system.
> >>
> >> I don't know how useful the tests are though -- while on a true SMP
> >> platform (ppc and x86 being available to me) they manage to fail quite
> >> realibly if I intentionally break something (like removing "lock"
> >> prefixes, or replacing stwcx. with an unconditional store), but it takes
> >> ages (if it works at all) to produce test failures on non-SMP (all
> >> threads to the same CPU).
> >
> > I recall someone once increasing the kernel's scheduling frequency to
> > make this work better.  On Linux, I think this means changing HZ and
> > recompiling the kernel.  Perhaps there is some trick that could be used
> > to force the kernel to reschedule more frequently without going to those
> > lengths.  Or maybe it is easier on some other platform.
> >
> > Even so, scheduling only happens between instructions, not between memory
> > accesses.  When a single instruction does more than one memory access
> > (i.e. a typical CISC instruction), process scheduling will never occur
> > between the two memory accesses.
>
> Maybe we should look at using Relacy (google for it) for tests.

It is only able to aid in exercising things that use the atomic interface, not 
the implementation itself.

Regards
Helge