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: Gottlob Frege (gottlobfrege_at_[hidden])
Date: 2011-08-06 01:40:02

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.

Tony