On Wed, Apr 11, 2012 at 15:02, Satyam Shekhar <[email protected]> wrote: >> The profiler is sampling based. That is, it wakes up at regular >> intervals (ticks) and records where the instruction pointer is. If the >> IP points to an address that cannot be resolved to a function, the >> tick is reported as unaccounted. > > Why does the IP need to point to a function? Can't it just point to any > instruction(line) in the function?
Yes, that's implied. :-) Say the profiler wakes up and finds that IP == 0x1234. It looks up that address in the program's symbol table and finds that the nearest function is foo@0x1230. The next nearest function is bar@0x1240, therefore the profiler knows we're in foo(). It's more involved than that but that's the essence of it. > I think m missing something very basic here.. It d help if you could tell me > when would this happen? Unaccounted ticks? For a variety of reasons. For example, glibc generates trampolines (executable on-stack code) that confuse the profiler no end. >> None. GC is accounted for separately under the (aptly named I daresay) >> section "GC": 36,598 ticks or 14.1% of total run time in your case. > > I doesn't look like it from the output. > > total ticks : 290423 > unaccounted ticks : 31441 > accounted ticks : 258982 > shared lib ticks : 194435 > javascript ticks : 64325 > GC ticks : 36598 > > shared lib + js ticks (258760 ) ~= accounted ticks(258982) (diff of 222 > ticks) I repeat: GC is accounted for *separately*. :-) > I mean when the profiler wakes up, it would look at a call trace right? Are > the lines logged in the JS section at the top of the stack? > This can be misleading since the call stack might have changed due to > setTimeouts. I want to understand how can I interpret these lines and what > are its caveats. That's how sample-based profiling works: you trade accuracy for efficiency. Here's a GSoC project for you: augment callgrind to understand the code V8 generates. I'll buy you a beer if you do. :-) -- Job Board: http://jobs.nodejs.org/ Posting guidelines: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines You received this message because you are subscribed to the Google Groups "nodejs" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nodejs?hl=en?hl=en
