[Pkg-openmpi-maintainers] Bug#598553: r-cran-rmpi: slave processes eat CPU when they have nothing to do

[Dirk Eddelbuettel]

Hi Zack,

On 29 September 2010 at 18:22, Zack Weinberg wrote:
| Package: r-cran-rmpi
| Version: 0.5-8-2
| Severity: normal
|
| Upon
| 
| > library(snow)
| > cl = makeCluster(7, type="MPI")
| 
| (on an 8-core machine), CPU utilization jumps *immediately* from 98% idle
| to 20% user, 70% system, 12% idle.  strace reveals that each slave is
| spinning through poll() calls with timeout zero, rather than blocking
| until a message arrives, as the documentation for mpi.probe() suggests
| should happen.
| 
| I suppose this might be a problem in libopenmpi instead of the R binding,
| I haven't tried to reproduce it with anything lower-level.

Very much so. It is "permanent polling" in Open MPI that does that --- and
Rmpi can do little about it.  So I think after some discussion we may want to
reassign or close this.

I used to be a little closer to Open MPI development (but now Manuel does
such wonderful work that I could step back from this :-) and there once was
word of changing.

Manuel, any idea if that happened?  Wasn't Open MPI 1.4 supposed to take care
of this?  Is there a new option?

Dirk

| 
| -- System Information:
| Debian Release: squeeze/sid
|   APT prefers unstable
|   APT policy: (500, 'unstable'), (101, 'experimental')
| Architecture: amd64 (x86_64)
| 
| Kernel: Linux 2.6.35-trunk-amd64 (SMP w/8 CPU cores)
| Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
| Shell: /bin/sh linked to /bin/dash
| 
| Versions of packages r-cran-rmpi depends on:
| ii  libc6                         2.11.2-6   Embedded GNU C Library: Shared lib
| ii  libopenmpi1.3                 1.4.2-4    high performance message passing l
| ii  mpi-default-bin               0.6        Standard MPI runtime programs
| ii  r-base-core                   2.11.1-6   GNU R core of statistical computat

New R 2.12.0 builds in experimental by the way.  I run those too. 2.12 will
come on October 15.


| 
| r-cran-rmpi recommends no packages.
| 
| Versions of packages r-cran-rmpi suggests:
| ii  r-cran-rsprng                 1.0-1      GNU R interface to SPRNG (Scalable
| 
| -- no debconf information
| 
| 

-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com