A bit more... >>stat (and others) do not really seem to be the problem. Darcs spends the >>most time waiting, spending roughly 96% of the time in __semwait_signal, >>most probably because of read_nocancel and select.
> How do we find out what this means? What's this __semwait_signal? Pieter on #macdev also said that the semaphore is probably being used for the read_nocancel and the select. OK then where do we go from here? Miserable is my low-level ignorance with undergrad CSE381 but a distant memory [1]. Whipping out /Advanced Programming in the UNIX Environment/, I see that there may be a concept of IO Multiplexing to grasp, and that the select() function * takes a set of descriptors you're interested in * waits until a descriptor is ready * returns which descriptors are ready OK... but what's the wider context here? What's causing these select() to be called and why? And what's this read_nocancel? >>the call numbers, __semwait_signal is called very rarely, compared to >>the calls to read, mmap, etc. Hmm... > OK, this bears highlighting: > > * that's 8 minutes out of 9 minutes fetching ghc locally in __semwait_signal > * a function which is called less than 6000 times (cf. 87000 stat) Err, hang on, that 8 minutes out of 9 number is bogus, sorry! I had dumbly plugged in "4474726631771 nanoseconds in minutes" into Google's converter tool but missed a digit. With the new 74 minute number, that can't mean what I assumed it meant. Then what do these times correspond to? > So this smells like the right kind of fishy. Is this the kind of thing > we may be able to just poke and suddenly find ourselves with dramatic > improvements on OS X? > Could the fancy graphical developer tools from Apple help with this at > all? Would the DTrace probles in GHC 6.13 help us to gain any insight? * http://hackage.haskell.org/trac/ghc/wiki/DTrace How about Instruments and Shark? * http://justtesting.org/profiling-garbage-collection-in-haskell-with * http://developer.apple.com/mac/library/DOCUMENTATION/DeveloperTools/Conceptual/InstrumentsUserGuide/Introduction/Introduction.html * http://www.jonathansaggau.com/blog/2008/09/using_shark_and_custom_dtrace.html [1] And if you happen to be in an undergraduate university setting taking a similar class <http://www.seas.upenn.edu/~cse381/>, pay more attention! It seems 1998-Eric's effort was woefully inadequate. -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> For a faster response, please try +44 (0)1273 64 2905.
signature.asc
Description: Digital signature
_______________________________________________ darcs-users mailing list darcs-users@darcs.net http://lists.osuosl.org/mailman/listinfo/darcs-users
