Re: Default value for numCapabilities?
On 28/04/2010 10:25, Dimitry Golubovsky wrote: Can the documentation for forkProcess be fixed then? Instead of forkProcess comes with a giant warning... it could say: forkProcess is not supported by GHC in multicore setting. Yes, will do. Cheers, Simon ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
On Tue, Apr 27, 2010 at 7:02 PM, Dimitry Golubovsky golubov...@gmail.comwrote: This is probably about forkProcess rather than forkIO/forkOS, but why this limitation? That's a standard Unix limitation. A child process is forked with one thread, so if the parent has multiple threads running, it's overwhelmingly likely that the child will be unable to execute correctly. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
On Wed, Apr 28, 2010 at 8:02 AM, Bryan O'Sullivan b...@serpentine.com wrote: On Tue, Apr 27, 2010 at 7:02 PM, Dimitry Golubovsky golubov...@gmail.com wrote: This is probably about forkProcess rather than forkIO/forkOS, but why this limitation? That's a standard Unix limitation. A child process is forked with one thread, so if the parent has multiple threads running, it's overwhelmingly likely that the child will be unable to execute correctly. One problem used to be that the I/O manager would get killed but Simon Marlow fixed that. I think we should support forking, with some caveats, so that we can daemonize processes. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
Simon, Can the documentation for forkProcess be fixed then? Instead of forkProcess comes with a giant warning... it could say: forkProcess is not supported by GHC in multicore setting. PS I have created ticket #4027 with more detailed proposal. On Wed, Apr 28, 2010 at 4:26 AM, Simon Marlow marlo...@gmail.com wrote: On 28/04/2010 03:02, Dimitry Golubovsky wrote: this limitation? rawSystem works fine from within a thread started by forkIO, but why cannot I use forkProcess? No good reason, other than it's tremendously difficult to implement. Thank you. -- Dimitry Golubovsky Anywhere on the Web ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Default value for numCapabilities?
Hi, As a followup to the discussion [1] about the portable way to find the number of CPUs/cores: how is the default value of numCapabilities [2] set when +RTS -N is not on the command line? Does GHC runtime figure out the number of cores itself, or it is by default 1 unless specified on the command line? Thanks. --- [1] http://haskell.org/pipermail/haskell-cafe/2010-April/076911.html [2] http://hackage.haskell.org/packages/archive/base/latest/doc/html/GHC-Conc.html#v:numCapabilities -- Dimitry Golubovsky Anywhere on the Web ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
On Tue, Apr 27, 2010 at 9:09 AM, Dimitry Golubovsky golubov...@gmail.comwrote: how is the default value of numCapabilities [2] set when +RTS -N is not on the command line? Does GHC runtime figure out the number of cores itself, With 6.12.1 and newer, no -N argument implies 1 core, -N*k* implies *k* cores, and -N without an argument means use all. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
Hello Dimitry, Tuesday, April 27, 2010, 8:09:49 PM, you wrote: a few months ago i asked SimonM about using all cores by default, but he said that it dramatically reduces performance in some cases Hi, As a followup to the discussion [1] about the portable way to find the number of CPUs/cores: how is the default value of numCapabilities [2] set when +RTS -N is not on the command line? Does GHC runtime figure out the number of cores itself, or it is by default 1 unless specified on the command line? Thanks. --- [1] http://haskell.org/pipermail/haskell-cafe/2010-April/076911.html [2] http://hackage.haskell.org/packages/archive/base/latest/doc/html/GHC-Conc.html#v:numCapabilities -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
Bulat, All I need is to know how many cores I have. In my program, I can run some actions in parallel, and knowing the number of cores helps set the maximum number of parallel processes. These processes are in fact external programs (CPU-intensive but not memory intensive, so number of cores is main factor) rather than GHC threads. I think I just need to check this experimentally as I have a 4-core (Atom) and 1-core (Via) PCs and see what numCapabilities returns. -- Dimitry Golubovsky Anywhere on the Web ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Default value for numCapabilities?
Hi, Interesting: my program is compiled with -threaded, and when I run it with +RTS -N I get: program name: forking not supported with +RTS -Nn greater than 1 This is probably about forkProcess rather than forkIO/forkOS, but why this limitation? rawSystem works fine from within a thread started by forkIO, but why cannot I use forkProcess? On Tue, Apr 27, 2010 at 12:35 PM, Bryan O'Sullivan b...@serpentine.com wrote: With 6.12.1 and newer, no -N argument implies 1 core, -Nk implies k cores, and -N without an argument means use all. -- Dimitry Golubovsky Anywhere on the Web ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
