what would be nice is to understand the amount of cpu time vs. the elapsed time consumed. you might be paging if you don't have sufficient real memory. I would venture a guess that the cpu time is very similar and the differnce is elapsed time due to some contention like memory.
Sent from my iPad On Jul 12, 2012, at 13:54, Ulrike Grömping <groemp...@bht-berlin.de> wrote: > 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.
