I obviously won't be in Dublin (I'll be in a fishing boat in the
middle of nowhere Canada -- much better), so I'm going to chime in now.
The m4 part actually isn't too bad and is pretty simple. I'm not sure
other than looking at some variables set by ompi_config_asm that there
is much to check. The hard parts are dealing with the finer grained
instruction set requirements.
On x86 in particular, many of the operations in the memcpy are part of
SSE, SSE2, or SSE3. Currently, we don't have any finer concept of a
processor than x86 and most compilers target an instruction set that
will run on anything considered 686, which is almost everything out
there. We'd have to decide how to handle instruction streams which
are no longer going to work on every chip. Since we know we have a
number of users with heterogeneous x86 clusters, this is something to
think about.
Brian
On Aug 17, 2008, at 7:57 AM, Jeff Squyres wrote:
Let's talk about this in Dublin. I can probably help with the m4
magic, but I need to understand exactly what needs to be done first.
On Aug 16, 2008, at 11:51 AM, Terry Dontje wrote:
George Bosilca wrote:
The intent of the memcpy framework is to allow a selection between
several memcpy at runtime. Of course, there will be a preselection
at compile time, but all versions that can compile on a given
architecture will be benchmarked at runtime and the best one will
be selected. There is a file with several versions of memcpy for
x86 (32 and 64) somewhere around (I should have one if
interested), that can be used as a starting point.
Ok, I guess I need to look at this code. I wonder if there may be
cases for Sun's machines in which this benchmark could end up
picking the wrong memcpy?
The only thing we need is a volunteer to build the m4 magic.
Figuring out what we can compile if kind of tricky, as some of the
functions are in assembly, some others in C, and some others a
mixture (the MMX headers).
Isn't the atomic code very similar? If I get to this point before
anyone else I probably will volunteer.
--td
george.
On Aug 16, 2008, at 3:19 PM, Terry Dontje wrote:
Hi Tim,
Thanks for bringing the below up and asking for a redirection to
the devel list. I think looking/using the MCA memcpy framework
would be a good thing to do and maybe we can work on this
together once I get out from under some commitments. However,
some of the challenges that originally scared me away from
looking at the memcpy MCA is whether we really want all the OMPI
memcpy's to be replaced or just specific ones. Also, I was
concerned on trying to figure out which version of memcpy I
should be using. I believe currently things are done such that
you get one version based on which system you compile on. For
Sun there may be several different SPARC platforms that would
need to use different memcpy code but we would like to just ship
one set of bits.
Not saying the above not doable under the memcpy MCA framework
just that it somewhat scared me away from thinking about it at
first glance.
--td
Date: Fri, 15 Aug 2008 12:08:18 -0400 From: "Tim Mattox" > Subject: Re: [OMPI users] SM btl slows down bandwidth? To:
"Open MPI Users" Message-ID: > Content-Type: text/plain; charset=ISO-8859-1 Hi Terry (and
others), I have previously explored this some on Linux/X86-64
and concluded that Open MPI needs to supply it's own memcpy
routine to get good sm performance, since the memcpy supplied by
glibc is not even close to optimal. We have an unused MCA
framework already set up to supply an opal_memcpy. AFAIK, George
and Brian did the original work to set up that framework. It has
been on my to-do list for awhile to start implementing
opal_memcpy components for the architectures I have access to,
and to modify OMPI to actually use opal_memcpy where ti makes
sense. Terry, I presume what you suggest could be dealt with
similarly when we are running/building on SPARC. Any followup
discussion on this should probably happen on the developer
mailing list. On Thu, Aug 14, 2008 at 12:19 PM, Terry Dontje > wrote:
> Interestingly enough on the SPARC platform the Solaris
memcpy's actually use
> non-temporal stores for copies >= 64KB. By default some of
the mca
> parameters to the sm BTL stop at 32KB. I've done
experimentations of
> bumping the sm segment sizes to above 64K and seen incredible
speedup on our
> M9000 platforms. I am looking for some nice way to integrate
a memcpy that
> lowers this boundary to 32KB or lower into Open MPI.
> I have not looked into whether Solaris x86/x64 memcpy's use
the non-temporal
> stores or not.
>
> --td
>>
>> Message: 1
>> Date: Thu, 14 Aug 2008 09:28:59 -0400
>> From: Jeff Squyres
>> Subject: Re: [OMPI users] SM btl slows down bandwidth?
>> To: rbbr...@sandia.gov, Open MPI Users
>> Message-ID: <562557eb-857c-4ca8-97ad-f294c7fed...@cisco.com>
>> Content-Type: text/plai
