My first guess would be there's not enough memory on the machine to support two of the tasks you're running, so swapping ensues.
--Todd -- Why is it so hard to remember the spelling of "mnemonic"? -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Ulrike Grömping Sent: Thursday, July 12, 2012 10:55 AM To: r-help@r-project.org Subject: [R] Two R sessions on multicore computer seem to inhibit each other ? Dear R-helpers, I am puzzled by the following observation: On my home dual core Windows desktop computer, I am used to running two R sessions in parallel. These do very well in using the full CPU of the computer (half each) and don't seem to slow each other down. Today I have started some large computation effort in one of our university labs, and I intended to go for two R sessions per computer as well. These computers are all identical and have Intel Core i5, 3.3 GHz processors with four cores, and they are used for my computations and nothing else at the moment. When I run one R session (32 bit) on them, the Windows task manager shows CPU usage at about 25%. If I add another R session that should also use as much CPU as it can get, the windows task manager showed overall CPU usage of the two sessions below 25%. This made me very suspicious, and I decided to use separate computers for all tasks (glad I did) and started a small investigation into what is going on here: one extra computer runs two R sessions that do the exact same calculations done on two other computers. I am surprised to see the enormous speed advantage of doing calculations on separate computers: a calculation that took 15 minutes on a computer that ran a single R session took 156 minutes in an R session on a computer with two R sessions running; the other example: 8 minutes to 71 minutes. Does anyone have any idea why running two R sessions simultaneously slows everything down so much? Thanks and regards, Ulrike -- View this message in context: http://r.789695.n4.nabble.com/Two-R-sessions-on-multicore-computer-seem-to-inhibit-each-other-tp4636336.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
