We made a big step forward today! The used Kernel has a bug regarding to the shared L1 instruction cache in AMD Bulldozer processors: See http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=dfb09f9b7ab03fd367740e541a5caf830ed56726 and http://developer.amd.com/Assets/SharedL1InstructionCacheonAMD15hCPU.pdf
Until the Kernel is patched we disable the address-space layout randomization (ASLR) as described in the above PDF: $ sudo /sbin/sysctl -w kernel.randomize_va_space=0 Therewith, NetPIPE results in ~0.5us latency when binding the processes for L2/L1I cache sharing (i.e. -bind-to-core). However, when binding the processes for exclusive L2/L1I caches (i.e. -cpus- per-proc 2) we still get ~1.1us latency. I don't think that the upcoming kernel patch will help for this kind of process binding... Matthias On Monday 12 March 2012 11:09:01 Matthias Jurenz wrote: > It's a SUSE Linux Enterprise Server 11 Service Pack 1 with kernel version > 2.6.32.49-0.3-default. > > Matthias > > On Friday 09 March 2012 16:36:41 you wrote: > > What OS are you using ? > > > > Joshua > > > > ----- Original Message ----- > > From: Matthias Jurenz [mailto:matthias.jur...@tu-dresden.de] > > Sent: Friday, March 09, 2012 08:50 AM > > To: Open MPI Developers <de...@open-mpi.org> > > Cc: Mora, Joshua > > Subject: Re: [OMPI devel] poor btl sm latency > > > > I just made an interesting observation: > > > > When binding the processes to two neighboring cores (L2 sharing) NetPIPE > > shows *sometimes* pretty good results: ~0.5us > > > > $ mpirun -mca btl sm,self -np 1 hwloc-bind -v core:0 ./NPmpi_ompi1.5.5 -u > > 4 -n 100000 -p 0 : -np 1 hwloc-bind -v core:1 ./NPmpi_ompi1.5.5 -u 4 -n > > 100000 -p 0 using object #0 depth 6 below cpuset 0xffffffff,0xffffffff > > using object #1 depth 6 below cpuset 0xffffffff,0xffffffff > > adding 0x00000001 to 0x0 > > adding 0x00000001 to 0x0 > > assuming the command starts at ./NPmpi_ompi1.5.5 > > binding on cpu set 0x00000001 > > adding 0x00000002 to 0x0 > > adding 0x00000002 to 0x0 > > assuming the command starts at ./NPmpi_ompi1.5.5 > > binding on cpu set 0x00000002 > > Using no perturbations > > > > 0: n035 > > Using no perturbations > > > > 1: n035 > > Now starting the main loop > > > > 0: 1 bytes 100000 times --> 6.01 Mbps in 1.27 usec > > 1: 2 bytes 100000 times --> 12.04 Mbps in 1.27 usec > > 2: 3 bytes 100000 times --> 18.07 Mbps in 1.27 usec > > 3: 4 bytes 100000 times --> 24.13 Mbps in 1.26 usec > > > > $ mpirun -mca btl sm,self -np 1 hwloc-bind -v core:0 ./NPmpi_ompi1.5.5 -u > > 4 -n 100000 -p 0 : -np 1 hwloc-bind -v core:1 ./NPmpi_ompi1.5.5 -u 4 -n > > 100000 -p 0 using object #0 depth 6 below cpuset 0xffffffff,0xffffffff > > adding 0x00000001 to 0x0 > > adding 0x00000001 to 0x0 > > assuming the command starts at ./NPmpi_ompi1.5.5 > > binding on cpu set 0x00000001 > > using object #1 depth 6 below cpuset 0xffffffff,0xffffffff > > adding 0x00000002 to 0x0 > > adding 0x00000002 to 0x0 > > assuming the command starts at ./NPmpi_ompi1.5.5 > > binding on cpu set 0x00000002 > > Using no perturbations > > > > 0: n035 > > Using no perturbations > > > > 1: n035 > > Now starting the main loop > > > > 0: 1 bytes 100000 times --> 12.96 Mbps in 0.59 usec > > 1: 2 bytes 100000 times --> 25.78 Mbps in 0.59 usec > > 2: 3 bytes 100000 times --> 38.62 Mbps in 0.59 usec > > 3: 4 bytes 100000 times --> 52.88 Mbps in 0.58 usec > > > > I can reproduce that approximately every tenth run. > > > > When binding the processes for exclusive L2 caches (e.g. core 0 and 2) I > > get constant latencies ~1.1us > > > > Matthias > > > > On Monday 05 March 2012 09:52:39 Matthias Jurenz wrote: > > > Here the SM BTL parameters: > > > > > > $ ompi_info --param btl sm > > > MCA btl: parameter "btl_base_verbose" (current value: <0>, data source: > > > default value) Verbosity level of the BTL framework > > > MCA btl: parameter "btl" (current value: <self,sm,openib>, data source: > > > file > > > [/sw/atlas/libraries/openmpi/1.5.5rc3/x86_64/etc/openmpi-mca-params.con > > > f] ) Default selection set of components for the btl framework (<none> > > > means use all components that can be found) > > > MCA btl: information "btl_sm_have_knem_support" (value: <1>, data > > > source: default value) Whether this component supports the knem Linux > > > kernel module or not > > > MCA btl: parameter "btl_sm_use_knem" (current value: <-1>, data source: > > > default value) Whether knem support is desired or not (negative = try > > > to enable knem support, but continue even if it is not available, 0 = > > > do not enable knem support, positive = try to enable knem support and > > > fail if it is not available) > > > MCA btl: parameter "btl_sm_knem_dma_min" (current value: <0>, data > > > source: default value) Minimum message size (in bytes) to use the knem > > > DMA mode; ignored if knem does not support DMA mode (0 = do not use the > > > knem DMA mode) MCA btl: parameter "btl_sm_knem_max_simultaneous" > > > (current value: <0>, data source: default value) Max number of > > > simultaneous ongoing knem operations to support (0 = do everything > > > synchronously, which probably gives the best large message latency; >0 > > > means to do all operations asynchronously, which supports better > > > overlap for simultaneous large message sends) > > > MCA btl: parameter "btl_sm_free_list_num" (current value: <8>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_free_list_max" (current value: <-1>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_free_list_inc" (current value: <64>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_max_procs" (current value: <-1>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_mpool" (current value: <sm>, data source: > > > default value) > > > MCA btl: parameter "btl_sm_fifo_size" (current value: <4096>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_num_fifos" (current value: <1>, data source: > > > default value) > > > MCA btl: parameter "btl_sm_fifo_lazy_free" (current value: <120>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_sm_extra_procs" (current value: <0>, data > > > source: default value) > > > MCA btl: parameter "btl_sm_exclusivity" (current value: <65535>, data > > > source: default value) BTL exclusivity (must be >= 0) > > > MCA btl: parameter "btl_sm_flags" (current value: <5>, data source: > > > default value) BTL bit flags (general flags: SEND=1, PUT=2, GET=4, > > > SEND_INPLACE=8, RDMA_MATCHED=64, HETEROGENEOUS_RDMA=256; flags only > > > used by the "dr" PML (ignored by others): ACK=16, CHECKSUM=32, > > > RDMA_COMPLETION=128; flags only used by the "bfo" PML (ignored by > > > others): FAILOVER_SUPPORT=512) MCA btl: parameter > > > "btl_sm_rndv_eager_limit" (current value: <4096>, data source: default > > > value) Size (in bytes) of "phase 1" fragment sent for all large > > > messages (must be >= 0 and <= eager_limit) > > > MCA btl: parameter "btl_sm_eager_limit" (current value: <4096>, data > > > source: default value) Maximum size (in bytes) of "short" messages > > > (must be >= 1). MCA btl: parameter "btl_sm_max_send_size" (current > > > value: <32768>, data source: default value) Maximum size (in bytes) of > > > a single "phase 2" fragment of a long message when using the pipeline > > > protocol (must be >= 1) > > > MCA btl: parameter "btl_sm_bandwidth" (current value: <9000>, data > > > source: default value) Approximate maximum bandwidth of interconnect(0 > > > = auto-detect value at run-time [not supported in all BTL modules], >= > > > 1 = bandwidth in Mbps) > > > MCA btl: parameter "btl_sm_latency" (current value: <1>, data source: > > > default value) Approximate latency of interconnect (must be >= 0) > > > MCA btl: parameter "btl_sm_priority" (current value: <0>, data source: > > > default value) > > > MCA btl: parameter "btl_base_warn_component_unused" (current value: > > > <1>, data source: default value) This parameter is used to turn on > > > warning messages when certain NICs are not used > > > > > > Matthias > > > > > > On Friday 02 March 2012 16:23:32 George Bosilca wrote: > > > > Please do a "ompi_info --param btl sm" on your environment. The > > > > lazy_free direct the internals of the SM BTL not to release the > > > > memory fragments used to communicate until the lazy limit is > > > > reached. The default value was deemed as reasonable a while back > > > > when the number of default fragments was large. Lately there were > > > > some patches to reduce the memory footprint of the SM BTL and these > > > > might have lowered the available fragments to a limit where the > > > > default value for the lazy_free is now too large. > > > > > > > > george. > > > > > > > > On Mar 2, 2012, at 10:08 , Matthias Jurenz wrote: > > > > > In thanks to the OTPO tool, I figured out that setting the MCA > > > > > parameter btl_sm_fifo_lazy_free to 1 (default is 120) improves the > > > > > latency significantly: 0,88µs > > > > > > > > > > But somehow I get the feeling that this doesn't eliminate the > > > > > actual problem... > > > > > > > > > > Matthias > > > > > > > > > > On Friday 02 March 2012 15:37:03 Matthias Jurenz wrote: > > > > >> On Friday 02 March 2012 14:58:45 Jeffrey Squyres wrote: > > > > >>> Ok. Good that there's no oversubscription bug, at least. :-) > > > > >>> > > > > >>> Did you see my off-list mail to you yesterday about building with > > > > >>> an external copy of hwloc 1.4 to see if that helps? > > > > >> > > > > >> Yes, I did - I answered as well. Our mail server seems to be > > > > >> something busy today... > > > > >> > > > > >> Just for the record: Using hwloc-1.4 makes no difference. > > > > >> > > > > >> Matthias > > > > >> > > > > >>> On Mar 2, 2012, at 8:26 AM, Matthias Jurenz wrote: > > > > >>>> To exclude a possible bug within the LSF component, I rebuilt > > > > >>>> Open MPI without support for LSF (--without-lsf). > > > > >>>> > > > > >>>> -> It makes no difference - the latency is still bad: ~1.1us. > > > > >>>> > > > > >>>> Matthias > > > > >>>> > > > > >>>> On Friday 02 March 2012 13:50:13 Matthias Jurenz wrote: > > > > >>>>> SORRY, it was obviously a big mistake by me. :-( > > > > >>>>> > > > > >>>>> Open MPI 1.5.5 was built with LSF support, so when starting an > > > > >>>>> LSF job it's necessary to request at least the number of > > > > >>>>> tasks/cores as used for the subsequent mpirun command. That was > > > > >>>>> not the case - I forgot the bsub's '-n' option to specify the > > > > >>>>> number of task, so only *one* task/core was requested. > > > > >>>>> > > > > >>>>> Open MPI 1.4.5 was built *without* LSF support, so the supposed > > > > >>>>> misbehavior could not happen with it. > > > > >>>>> > > > > >>>>> In short, there is no bug in Open MPI 1.5.x regarding to the > > > > >>>>> detection of oversubscription. Sorry for any confusion! > > > > >>>>> > > > > >>>>> Matthias > > > > >>>>> > > > > >>>>> On Tuesday 28 February 2012 13:36:56 Matthias Jurenz wrote: > > > > >>>>>> When using Open MPI v1.4.5 I get ~1.1us. That's the same > > > > >>>>>> result as I get with Open MPI v1.5.x using > > > > >>>>>> mpi_yield_when_idle=0. So I think there is a bug in Open MPI > > > > >>>>>> (v1.5.4 and v1.5.5rc2) regarding to the automatic performance > > > > >>>>>> mode selection. > > > > >>>>>> > > > > >>>>>> When enabling the degraded performance mode for Open MPI 1.4.5 > > > > >>>>>> (mpi_yield_when_idle=1) I get ~1.8us latencies. > > > > >>>>>> > > > > >>>>>> Matthias > > > > >>>>>> > > > > >>>>>> On Tuesday 28 February 2012 06:20:28 Christopher Samuel wrote: > > > > >>>>>>> On 13/02/12 22:11, Matthias Jurenz wrote: > > > > >>>>>>>> Do you have any idea? Please help! > > > > >>>>>>> > > > > >>>>>>> Do you see the same bad latency in the old branch (1.4.5) ? > > > > >>>>>>> > > > > >>>>>>> cheers, > > > > >>>>>>> Chris > > > > >>>>>> > > > > >>>>>> _______________________________________________ > > > > >>>>>> devel mailing list > > > > >>>>>> de...@open-mpi.org > > > > >>>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > > >>>>> > > > > >>>>> _______________________________________________ > > > > >>>>> devel mailing list > > > > >>>>> de...@open-mpi.org > > > > >>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > > >>>> > > > > >>>> _______________________________________________ > > > > >>>> devel mailing list > > > > >>>> de...@open-mpi.org > > > > >>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > > >> > > > > >> _______________________________________________ > > > > >> devel mailing list > > > > >> de...@open-mpi.org > > > > >> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > > > > > > > > _______________________________________________ > > > > > devel mailing list > > > > > de...@open-mpi.org > > > > > http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > > > > > > _______________________________________________ > > > > devel mailing list > > > > de...@open-mpi.org > > > > http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > > > > _______________________________________________ > > > devel mailing list > > > de...@open-mpi.org > > > http://www.open-mpi.org/mailman/listinfo.cgi/devel > > _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel
