> -----Original Message----- > From: Mark Hahn [mailto:[EMAIL PROTECTED] > Sent: Tuesday, June 12, 2007 6:15 PM > To: Tahir Malas > Cc: [EMAIL PROTECTED]; beowulf@beowulf.org; > [EMAIL PROTECTED]; 'Ozgur Ergul' > Subject: Re: [Beowulf] Two problems related to slowness and > TASK_UNINTERRUPTABLE process > > > For 32 processes (4 process per node), the arrays with 512-Byte size are > > communicated slower than the 4096-Byte size arrays. For both of them, we > > do you mean that this is not the case in other configurations? > an interconnect _should_ have some steep rise in effective bandwidth > as packet size is increased. it's a useful metric to know the packet > size at which half-peak bandwidth is achieved, since this offers some > "sense of scale" to programmers judging whether their own packet sizes > are appropriate.
> > > this abnormal case is persistent. More specifically, communication of > > 4k-Byte packages are 2 times faster than the communication of 512-Byte > > packages. > > perhaps I'm dense this morning, but what's unexpected about that? Considering the latency and bw measures, my expectation for the communication times in us: 512: 5.48 + 512/592.34 = 6.34 4096: 11.02 + 4096/906.04 = 15.54 Our test: 512: 29.434 4096: 16.209 So, somehow, isn't communication time for 512 bytes is unexpectedly slow? > > > > 2. SOMETIMES, after the test with overall 32 processes, one of the four > > processes at node3 hangs in TASK_UNINTERRUPTABLE "D" state. Hence, the > test > > program shows a "done." and waits for sometime. We can neither kill the > > process nor soft reboot the node. We have to wait for that process to > > terminate, which can last long. > > does /proc/$pid/wchan (on the 'D' state process) tell you anything? > do all the ranks return from MPI_Finalize? > The file tells "__lock_buffer". Yes, all ranks return; but I think, this problematic process (i.e. one of the processes on node3) returns always the latest. Thanks, and regards, Tahir. _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
