Some potentially-interesting links (of which I understand very little): http://stackoverflow.com/questions/860602/recommended-open-source-profilers#comment2363112_1137133 http://stackoverflow.com/questions/8406175/optimizing-stack-walking-performance
I can tell from this comment: https://github.com/JuliaLang/julia/issues/2597#issuecomment-15159868 that you already know about this (and its negatives): http://www.lenholgate.com/blog/2008/09/alternative-call-stack-capturing.html --Tim On Wednesday, December 03, 2014 02:25:22 PM Jameson Nash wrote: > this stack overflow question indicates that there are two options ( > http://stackoverflow.com/questions/153559/what-are-some-good-profilers-for-n > ative-c-on-windows ) > > https://software.intel.com/sites/default/files/managed/cd/92/Intel-VTune-Amp > lifierXE-2015-Product-Brief-072914.pdf ($900) > http://www.glowcode.com/summary.htm ($500) > > > On Wed Dec 03 2014 at 9:11:28 AM Stefan Karpinski <[email protected]> > > wrote: > > This seems nuts. There have to be good profilers on Windows – how do those > > work? > > > > On Tue, Dec 2, 2014 at 11:55 PM, Jameson Nash <[email protected]> wrote: > >> (I forgot to mention, that, to be fair, the windows machine that was used > >> to run this test was an underpowered dual-core hyperthreaded atom > >> processor, whereas the linux and mac machines were pretty comparable Xeon > >> and sandybridge machines, respectively. I only gave windows a factor of 2 > >> advantage in the above computation in my accounting for this gap) > >> > >> On Tue Dec 02 2014 at 10:50:20 PM Tim Holy <[email protected]> wrote: > >>> Wow, those are pathetically-slow backtraces. Since most of us don't have > >>> machines with 500 cores, I don't see anything we can do. > >>> > >>> --Tim > >>> > >>> On Wednesday, December 03, 2014 03:14:02 AM Jameson Nash wrote: > >>> > you could copy the whole stack (typically only a few 100kb, max of > >>> > >>> 8MB), > >>> > >>> > then do the stack walk offline. if you could change the stack pages to > >>> > copy-on-write, it may even not be too expensive. > >>> > > >>> > but this is the real problem: > >>> > > >>> > ``` > >>> > > >>> > |__/ | x86_64-linux-gnu > >>> > > >>> > julia> @time for i=1:10^4 backtrace() end > >>> > elapsed time: 2.789268693 seconds (3200320016 bytes allocated, 89.29% > >>> > >>> gc > >>> > >>> > time) > >>> > ``` > >>> > > >>> > ``` > >>> > > >>> > |__/ | x86_64-apple-darwin14.0.0 > >>> > > >>> > julia> @time for i=1:10^4 backtrace() end > >>> > elapsed time: 2.586410216 seconds (6400480000 bytes allocated, 89.96% > >>> > >>> gc > >>> > >>> > time) > >>> > ``` > >>> > > >>> > ``` > >>> > jameson@julia:~/julia-win32$ ./usr/bin/julia.exe -E " @time for > >>> > >>> i=1:10^3 > >>> > >>> > backtrace() end " > >>> > fixme:winsock:WS_EnterSingleProtocolW unknown Protocol <0x00000000> > >>> > fixme:winsock:WS_EnterSingleProtocolW unknown Protocol <0x00000000> > >>> > err:dbghelp_stabs:stabs_parse Unknown stab type 0x0a > >>> > elapsed time: 22.6314386 seconds (320032016 bytes allocated, 1.51% gc > >>> > >>> time) > >>> > >>> > ``` > >>> > > >>> > ``` > >>> > > >>> > |__/ | i686-w64-mingw32 > >>> > > >>> > julia> @time for i=1:10^4 backtrace() end > >>> > elapsed time: 69.243275608 seconds (3200320800 bytes allocated, 13.16% > >>> > >>> gc > >>> > >>> > time) > >>> > ``` > >>> > > >>> > And yes, those gc fractions are verifiably correct. With gc_disable(), > >>> > >>> they > >>> > >>> > execute in 1/10 of the time. So, that pretty much means you must take > >>> > >>> 1/100 > >>> > >>> > of the samples if you want to preserve roughly the same slow down. On > >>> > linux, I find the slowdown to be in the range of 2-5x, and consider > >>> > >>> that to > >>> > >>> > be pretty reasonable, especially for what you're getting. If you took > >>> > >>> the > >>> > >>> > same number of samples on windows, it would cause a 200-500x slowdown > >>> > >>> (give > >>> > >>> > or take a few percent). If you wanted to offload this work to other > >>> > >>> cores > >>> > >>> > to get the same level of accuracy and no more slowdown than linux, you > >>> > would need a machine with 200-500 processors (give or take 2-5)! > >>> > > >>> > (I think I did those conversions correctly. However, since I just did > >>> > >>> them > >>> > >>> > for the purposes of this email, sans calculator, and as I was typing, > >>> > >>> let > >>> > >>> > me know if I made more than a factor of 2 error somewhere, or just > >>> > >>> have fun > >>> > >>> > reading https://what-if.xkcd.com/84/ instead) > >>> > > >>> > On Tue Dec 02 2014 at 6:23:07 PM Tim Holy <[email protected]> wrote: > >>> > > On Tuesday, December 02, 2014 10:24:43 PM Jameson Nash wrote: > >>> > > > You can't profile a moving target. The thread must be frozen first > >>> > >>> to > >>> > >>> > > > ensure the stack trace doesn't change while attempting to record > >>> > > > it > >>> > > > >>> > > Got it. I assume there's no good way to "make a copy and then > >>> > >>> discard if > >>> > >>> > > the > >>> > > copy is bad"? > >>> > > > >>> > > --Tim > >>> > > > >>> > > > On Tue, Dec 2, 2014 at 5:12 PM Tim Holy <[email protected]> > >>> > >>> wrote: > >>> > > > > If the work of walking the stack is done in the thread, why does > >>> > >>> it > >>> > >>> > > cause > >>> > > > >>> > > > > any > >>> > > > > slowdown of the main process? > >>> > > > > > >>> > > > > But of course the time it takes to complete the backtrace sets > >>> > > > > an > >>> > > > > upper > >>> > > > > limit > >>> > > > > on how frequently you can take a snapshot. In that case, though, > >>> > > > >>> > > couldn't > >>> > > > >>> > > > > you > >>> > > > > just have the thread always collecting backtraces? > >>> > > > > > >>> > > > > --Tim > >>> > > > > > >>> > > > > On Tuesday, December 02, 2014 09:54:17 PM Jameson Nash wrote: > >>> > > > > > That's essentially what we do now. (Minus the busy wait part). > >>> > >>> The > >>> > >>> > > > > overhead > >>> > > > > > >>> > > > > > is too high to run it any more frequently -- it already causes > >>> > >>> a > >>> > >>> > > > > > significant performance penalty on the system, even at the > >>> > > > > > much > >>> > > > > > lower > >>> > > > > > sample rate than linux. However, I suspect the truncated > >>> > >>> backtraces > >>> > >>> > > on > >>> > > > >>> > > > > > win32 were exaggerating the effect somewhat -- that should not > >>> > >>> be as > >>> > >>> > > > > > much > >>> > > > > > of an issue now. > >>> > > > > > > >>> > > > > > Sure, windows lets you snoop on (and modify) the address space > >>> > >>> of > >>> > >>> > > > > > any > >>> > > > > > process, you just need to find the right handle. > >>> > > > > > > >>> > > > > > On Tue, Dec 2, 2014 at 2:18 PM Tim Holy <[email protected]> > >>> > >>> wrote: > >>> > > > > > > On Windows, is there any chance that one could set up a > >>> > >>> separate > >>> > >>> > > > > > > thread > >>> > > > > > > for > >>> > > > > > > profiling and use busy-wait to do the timing? (I don't even > >>> > >>> know > >>> > >>> > > > > whether > >>> > > > > > >>> > > > > > > one > >>> > > > > > > thread can snoop on the execution state of another thread.) > >>> > > > > > > > >>> > > > > > > --Tim > >>> > > > > > > > >>> > > > > > > On Tuesday, December 02, 2014 06:22:39 PM Jameson Nash wrote: > >>> > > > > > > > Although, over thanksgiving, I pushed a number of fixes > >>> > >>> which > >>> > >>> > > should > >>> > > > >>> > > > > > > > improve the quality of backtraces on win32 (and make > >>> > >>> sys.dll > >>> > >>> > > usable > >>> > > > >>> > > > > > > there) > >>> > > > > > > > >>> > > > > > > > On Tue, Dec 2, 2014 at 1:20 PM Jameson Nash < > >>> > >>> [email protected]> > >>> > >>> > > > > wrote: > >>> > > > > > > > > Correct. Windows imposes a much higher overhead on just > >>> > >>> about > >>> > >>> > > > > > > > > every > >>> > > > > > > > >>> > > > > > > aspect > >>> > > > > > > > >>> > > > > > > > > of doing profiling. Unfortunately, there isn't much we > >>> > >>> can do > >>> > >>> > > > > > > > > about > >>> > > > > > > > >>> > > > > > > this, > >>> > > > > > > > >>> > > > > > > > > other then to complain to Microsoft. (It doesn't have > >>> > >>> signals, > >>> > >>> > > so > >>> > > > >>> > > > > we > >>> > > > > > >>> > > > > > > must > >>> > > > > > > > >>> > > > > > > > > emulate them with a separate thread. The accuracy of > >>> > >>> windows > >>> > >>> > > > > timers is > >>> > > > > > >>> > > > > > > > > somewhat questionable. And the stack walk library (for > >>> > > > >>> > > recording > >>> > > > >>> > > > > the > >>> > > > > > >>> > > > > > > > > backtrace) is apparently just badly written and > >>> > > > > > > > > therefore > >>> > > > >>> > > insanely > >>> > > > >>> > > > > > > > > slow > >>> > > > > > > > > and > >>> > > > > > > > > memory hungry.) > >>> > > > > > > > > > >>> > > > > > > > > On Tue, Dec 2, 2014 at 12:59 PM Tim Holy < > >>> > >>> [email protected]> > >>> > >>> > > > > wrote: > >>> > > > > > > > >> I think it's just that Windows is bad at scheduling > >>> > >>> tasks > >>> > >>> > > > > > > > >> with > >>> > > > > > > > >> short-latency, > >>> > > > > > > > >> high-precision timing, but I am not the right person to > >>> > > > > > > > >> answer > >>> > > > > > >>> > > > > such > >>> > > > > > >>> > > > > > > > >> questions. > >>> > > > > > > > >> > >>> > > > > > > > >> --Tim > >>> > > > > > > > >> > >>> > > > > > > > >> On Tuesday, December 02, 2014 09:57:28 AM Peter Simon > >>> > >>> wrote: > >>> > > > > > > > >> > I have also experienced the inaccurate profile > >>> > >>> timings on > >>> > >>> > > > > Windows. > >>> > > > > > >>> > > > > > > Is > >>> > > > > > > > >>> > > > > > > > >> the > >>> > > > > > > > >> > >>> > > > > > > > >> > reason for the bad profiler performance on Windows > >>> > > > >>> > > understood? > >>> > > > >>> > > > > Are > >>> > > > > > >>> > > > > > > > >> there > >>> > > > > > > > >> > >>> > > > > > > > >> > plans for improvement? > >>> > > > > > > > >> > > >>> > > > > > > > >> > Thanks, > >>> > > > > > > > >> > --Peter > >>> > > > > > > > >> > > >>> > > > > > > > >> > On Tuesday, December 2, 2014 3:57:16 AM UTC-8, Tim > >>> > >>> Holy > >>> > >>> > > wrote: > >>> > > > > > > > >> > > By default, the profiler takes one sample per > >>> > > > >>> > > millisecond. In > >>> > > > >>> > > > > > > > >> practice, > >>> > > > > > > > >> > >>> > > > > > > > >> > > the > >>> > > > > > > > >> > > timing is quite precise on Linux, seemingly within > >>> > > > > > > > >> > > a > >>> > > > >>> > > factor > >>> > > > >>> > > > > > > > >> > > of > >>> > > > > > > > >>> > > > > > > twoish > >>> > > > > > > > >>> > > > > > > > >> on > >>> > > > > > > > >> > >>> > > > > > > > >> > > OSX, > >>> > > > > > > > >> > > and nowhere close on Windows. So at least on Linux > >>> > >>> you > >>> > >>> > > > > > > > >> > > can > >>> > > > > > >>> > > > > simply > >>> > > > > > >>> > > > > > > > >> > > read > >>> > > > > > > > >> > > samples > >>> > > > > > > > >> > > as milliseconds. > >>> > > > > > > > >> > > > >>> > > > > > > > >> > > If you want to visualize the relative contributions > >>> > >>> of > >>> > >>> > > each > >>> > > > >>> > > > > > > > >> statement, I > >>> > > > > > > > >> > >>> > > > > > > > >> > > highly recommend ProfileView. If you use > >>> > >>> LightTable, it's > >>> > >>> > > > > already > >>> > > > > > >>> > > > > > > > >> built-in > >>> > > > > > > > >> > >>> > > > > > > > >> > > via > >>> > > > > > > > >> > > the profile() command. The combination of > >>> > >>> ProfileView and > >>> > >>> > > > > > > > >> > > @profile > >>> > > > > > > > >> > >>> > > > > > > > >> is, in > >>> > > > > > > > >> > >>> > > > > > > > >> > > my > >>> > > > > > > > >> > > (extremely biased) opinion, quite powerful compared > >>> > >>> to > >>> > >>> > > tools > >>> > > > >>> > > > > > > > >> > > I > >>> > > > > > > > >>> > > > > > > used > >>> > > > > > > > >>> > > > > > > > >> > > previously > >>> > > > > > > > >> > > in other programming environments. > >>> > > > > > > > >> > > > >>> > > > > > > > >> > > Finally, there's IProfile.jl, which works via a > >>> > > > > > > > >> > > completely > >>> > > > > > > > >>> > > > > > > different > >>> > > > > > > > >>> > > > > > > > >> > > mechanism > >>> > > > > > > > >> > > but does report raw timings (with some pretty big > >>> > > > >>> > > caveats). > >>> > > > >>> > > > > > > > >> > > Best, > >>> > > > > > > > >> > > --Tim > >>> > > > > > > > >> > > > >>> > > > > > > > >> > > On Monday, December 01, 2014 10:13:16 PM Christoph > >>> > >>> Ortner > >>> > >>> > > > > wrote: > >>> > > > > > > > >> > > > How do you get timings from the Julia profiler, > >>> > >>> or even > >>> > >>> > > > > better, > >>> > > > > > >>> > > > > > > > >> %-es? I > >>> > > > > > > > >> > >>> > > > > > > > >> > > > guess one can convert from the numbers one gets, > >>> > >>> but it > >>> > >>> > > is > >>> > > > >>> > > > > > > > >> > > > a > >>> > > > > > > > >> > > > bit > >>> > > > > > > > >> > > > >>> > > > > > > > >> > > painful? > >>> > > > > > > > >> > > > >>> > > > > > > > >> > > > Christoph
