notes on v8

notesonv8.txt

https://www.youtube.com/watch?v=VhpdsjBUS3g&feature=youtu.be&t=16m30s
http://mrale.ph/blog/2011/12/18/v8-optimization-checklist.html

gdb compile
https://groups.google.com/forum/#!topic/v8-users/OIICvStFMmc
https://groups.google.com/forum/#!searchin/v8-users/gdb%7Csort:relevance/v8-users/GxCmg3fRaLU/p6Jb95RkQ9cJ

V8 Inside Out” from WebRebels 2012

saw tooth gc memory usage

v8 gc trigger
memory pool is exhausted and need to allocate
young and old memory, age based on gc survived
young, fast allocation,collection and freqention collection
	few survive,(80%)
old generation slow and infrequent
	increment mark,sweep(return memory), compact

young space
	to and from space
		to ( new Foo)
		unllocated memory
	when your try to allocate and run out of space
		swap to and from
		mark used memory in from space
		copy back to "to space"

issues 
	calling new
	unoptmized mode code 
		implicit memory allocation ex each math op
		var a = p*x two allocations

		v8 will eventually try to optomize code
		code can be deoptimized
		to many deoptimzations cause code to never be optmized
		try catch not optimized

	modify objects
		add field to existing object
		deoptimized
		new class is generate in v8

v8 tools
	v8 timeline
		--prof --noprof-lazy --log-timer-events
		plot-timer-events
			generate png file
			state v8 is in
			code kind
				optimized and unoptimized
				green optimized
				blue and red unoptimized
		--prof --noprof-lazy --log-timer-events
		<os>-tick-proccesor
			functions seen by profiler
			* shows optimized
			~ unoptimized

		find unoptimized functions
		--trace-deopt --trace-opt-verbose
		text to terminal
		optimization and reason

ic
inline cache
	ic-explorer.html
__

The corresponding source can be found in
  src/heap/gc-tracer.cc

On Wed, Sep 16, 2015 at 7:02 AM dmonji <[email protected]> wrote:
[29648:0xbad6f48]     2631 ms: Scavenge 8.0 (22.6) -> 4.2 (22.6) MB, 8.4 / 0 ms [allocation failure].

[<process id>:<isolate address>] <absolute time> ms: <type> <start object size> (<start memory size>) -> <end object size> (<end memory size>) MB, <scavenge duration> / <time spent in external callbacks, e.g. embedder> [<reason>].
 
[29648:0xbad6f48]     3130 ms: Mark-sweep 8.0 (22.6) -> 4.4 (22.6) MB, 63.0 / 0 ms (+ 69.0 ms in 55 steps since start of marking, biggest step 2.4 ms) [GC interrupt] [GC in old space requested].


Same as above, with the addition
  ... (<time spent in incremental marking> / <# incremental steps> , biggest step <longest time for incremental marking step>) [<reason, e.g. GC via stack guard] [<ultimate reason>].


g++ -o shell src/hello-world.cc -I. -I./deps/v8 -I./deps/v8/include -I./include -Wl,--start-group deps/v8/out/x64.release/obj.target/{src/libv8_{base,libbase,external_snapshot,libplatform,libsampler},third_party/icu/libicu{uc,i18n}}.a -Wl,--end-group -lrt -ldl -pthread -std=c++0x