Profiling and optimizing go programs

5/12/2016 Proﬁling and optimizing Go programs
http://localhost:3999/gomeetup.slide#1 1/84
Pro ling and optimizing Go
programs
14 July 2016
Marko Kevac
Software Engineer, Badoo

Introduction

What is pro ling and optimization?

Pro ling on Linux

Pro ling on OSX
OSX pro ling xed in El Capitan.
Previous versions need binary patch.
godoc.org/rsc.io/pprof_mac_ x(https://godoc.org/rsc.io/pprof_mac_ x)

CPU
github.com/gperftools/gperftools(https://github.com/gperftools/gperftools)

CPU
pprof is a sampling pro ler.
All pro lers in Go can be started in a di erent ways, but all of them can be broken into
collection and visualization phase.
Example.

Example
packageperftest
import(
"regexp"
"strings"
"testing"
)
varhaystack=`Loremipsumdolorsitamet...auctor...elit...`
funcBenchmarkSubstring(b*testing.B){
fori:=0;i<b.N;i++{
strings.Contains(haystack,"auctor")
}
}
funcBenchmarkRegex(b*testing.B){
fori:=0;i<b.N;i++{
regexp.MatchString("auctor",haystack)
}
}

Benchmark
$gotest-bench=.
testing:warning:noteststorun
BenchmarkSubstring-8 10000000 194ns/op
BenchmarkRegex-8 200000 7516ns/op
PASS
ok github.com/mkevac/perftest00 3.789s

Pro ling
$GOGC=offgotest-bench=BenchmarkRegex-cpuprofilecpu.out
PASS
GOGC=o turns o garbage collector
Turning o GC can be bene cial for short programs.
When started with -cpupro le, go test puts binary in our working dir.

Visualization
Linux
$gotoolpprofperftest00.testcpu.out
(pprof)web
OSX
$openhttps://www.xquartz.org
$ssh-Yserver
$gotoolpprofperftest00.testcpu.out
(pprof)web
Other
$gotoolpprof-svg./perftest00.test./cpu.out>cpu.svg
$scp...
$opencpu.svg

Visualization

Fix
packageperftest
import(
"regexp"
"strings"
"testing"
)
varpattern=regexp.MustCompile("auctor")
funcBenchmarkSubstring(b*testing.B){
fori:=0;i<b.N;i++{
strings.Contains(haystack,"auctor")
}
}
funcBenchmarkRegex(b*testing.B){
fori:=0;i<b.N;i++{
pattern.MatchString(haystack)
}
}

Benchmark
$gotest-bench=.
BenchmarkSubstring-8 10000000 170ns/op
PASS
What about call graph?

Visualization
We don't see compilation at all.

Ways to start CPU pro ler
1. go test -cpupro le=cpu.out
2. pprof.StartCPUPro le() and pprof.StopCPUPro le() or Dave Cheney great package
github.com/pkg/pro le(https://github.com/pkg/pro le)
3. import _ "net/http/pprof"
Example

Example
packagemain
import(
"net/http"
_"net/http/pprof"
)
funccpuhogger(){
varaccuint64
for{
acc+=1
ifacc&1==0{
acc<<=1
}
}
}
funcmain(){
gohttp.ListenAndServe("0.0.0.0:8080",nil)
cpuhogger()
}

Visualization
$gotoolpprofhttp://localhost:8080/debug/pprof/profile?seconds=5
(pprof)web
(pprof)top
4.99sof4.99stotal( 100%)
flat flat% sum% cum cum%
4.99s 100% 100% 4.99s 100% main.cpuhogger
0 0% 100% 4.99s 100% runtime.goexit
0 0% 100% 4.99s 100% runtime.main
(pprof)listcpuhogger
Total:4.99s
Nosourceinformationformain.cpuhogger
No disassembly? No source code? We need binary.

Visualization
$gotoolpprofpproftesthttp://localhost:8080/debug/pprof/profile?seconds=5
(pprof)listcpuhogger
Total:4.97s
ROUTINE========================main.cpuhoggerin/home/marko/goprojects/src/github.com/mkevac/pproft
4.97s 4.97s(flat,cum) 100%ofTotal
. . 6:)
. . 7:
. . 8:funccpuhogger(){
. . 9: varaccuint64
. . 10: for{
2.29s 2.29s 11: acc+=1
1.14s 1.14s 12: ifacc&1==0{
1.54s 1.54s 13: acc<<=1
. . 14: }
. . 15: }
. . 16:}
. . 17:
. . 18:funcmain(){

Visualization
(pprof)disasmcpuhogger
Total:4.97s
ROUTINE========================main.cpuhogger
4.97s 4.97s(flat,cum) 100%ofTotal
. . 401000:XORLAX,AX
1.75s 1.75s 401002:INCQAX
1.14s 1.14s 401005:TESTQ$0x1,AX
. . 40100b:JNE0x401002
1.54s 1.54s 40100d:SHLQ$0x1,AX
540ms 540ms 401010:JMP0x401002
. . 401012:INT$0x3
Why? Let's dig deeper.

Why?
$curlhttp://localhost:8080/debug/pprof/profile?seconds=5-o/tmp/cpu.log
$strings/tmp/cpu.log|grepcpuhogger
/debug/pprof/symbol for acquiring symbols
binary for disassembly
binary and source code for source code
Currently there is no way to specify path to source code (same as "dir" command in
gdb) :-(
Binary that you give to pprof and binary that is running must be the same!
Not deep enough?

How pprof works?
1. Current desktop and server OS's implement preemptive scheduling
(https://en.wikipedia.org/wiki/Preemption_(computing))or preemptive multitasking (oposing to cooperative
multitasking).
2. Hardware sends signal to OS and OS executes scheduler which can preempt
working process and put other process on it's place.
3. pprof works in similar fashion.
4. man setitimer(http://man7.org/linux/man-pages/man2/setitimer.2.html)and SIGPROF
5. Go sets handler for SIGPROF which gets and saves stack traces for all
goroutines/threads.
6. Separate goroutine gives this data to user.
Bug in SIGPROF signal delivery(http://research.swtch.com/macpprof)was the reason why pro ling on OSX
pre El Capitain did not work.

How pprof works?
Cons
1. Signals are not cheap. Do not expect more than 500 signals per second. Default
frequency in Go runtime is 100 HZ.
2. In non standard builds (-buildmode=c-archive or -buildmode=c-shared) pro ler do
not work by default.
3. User space process do not have access to kernel stack trace.
Pros
Go runtime has all the knowledge about internal stu .

Linux system pro lers
funcUsingSubstring()bool{
found:=strings.Contains(haystack,"auctor")
returnfound
}
funcUsingRegex()bool{
found,_:=regexp.MatchString("auctor",haystack)
returnfound
}
funcmain(){
gofunc(){
for{
UsingSubstring()
}
}()
for{
UsingRegex()
}
}

Systemtap
Systemtap script -> C code -> Kernel module
stap utility do all these things for you. Including kernel module loading and unloading.

Systemtap
Getting probe list:
$stap-l'process("systemtap").function("main.*")'
process("systemtap").function("main.UsingRegex@main.go:16")
process("systemtap").function("main.UsingSubstring@main.go:11")
process("systemtap").function("main.init@main.go:32")
process("systemtap").function("main.main.func1@main.go:22")
process("systemtap").function("main.main@main.go:21")
Getting probe list with function arguments
$stap-L'process("systemtap").function("runtime.mallocgc")'
process("systemtap").function("runtime.mallocgc@src/runtime/malloc.go:553")
$shouldhelpgc:bool$noscan:bool$scanSize:uintptr$dataSize:uintptr$x:void*$s:structruntime.mspan*
runtime.g*$size:uintptr$typ:runtime._type*$needzero:bool$~r3:void*
Systemtap do not understand where Go keeps return value, so we can get in
manually:
printf("%dn",user_int64(register("rsp")+8))

Systemtap
globaletime
globalintervals
probe$1.call {
etime=gettimeofday_ns()
}
probe$1.return{
intervals<<<(gettimeofday_ns()-etime)/1000
}
probeend{
printf("Durationmin:%dusavg:%dusmax:%duscount:%dn",
@min(intervals),@avg(intervals),@max(intervals),
@count(intervals))
printf("Duration(us):n")
print(@hist_log(intervals));
printf("n")
}

Systemtap
$sudostapmain.stap'process("systemtap").function("main.UsingSubstring")'
^CDurationmin:0usavg:1usmax:586uscount:1628362
Duration(us):
value|--------------------------------------------------count
0| 10
1|@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1443040
2|@@@@@ 173089
4| 6982
8| 4321
16| 631
32| 197
64| 74
128| 13
256| 4
512| 1
1024| 0
2048| 0

Systemtap
$./systemtap
runtime:unexpectedreturnpcformain.UsingSubstringcalledfrom0x7fffffffe000
fatalerror:unknowncallerpc
runtimestack:
runtime.throw(0x494e40,0x11)
/home/marko/go/src/runtime/panic.go:566+0x8b
runtime.gentraceback(0xffffffffffffffff,0xc8200337a8,0x0,0xc820001d40,0x0,0x0,0x7fffffff,0x7fff
/home/marko/go/src/runtime/traceback.go:311+0x138c
runtime.scanstack(0xc820001d40)
/home/marko/go/src/runtime/mgcmark.go:755+0x249
runtime.scang(0xc820001d40)
/home/marko/go/src/runtime/proc.go:836+0x132
runtime.markroot.func1()
/home/marko/go/src/runtime/mgcmark.go:234+0x55
runtime.systemstack(0x4e4f00)
/home/marko/go/src/runtime/asm_amd64.s:298+0x79
runtime.mstart()
/home/marko/go/src/runtime/proc.go:1087

Systemtap
Crash when Go's garbage collector gets its call trace.
Probably caused by trampoline that systemtap puts in our code to handle its probes.
goo.gl/N8XH3p(https://goo.gl/N8XH3p)
No x yet.
But Go is not alone. There are problems with uretprobes trampoline in C++ too
(https://sourceware.org/bugzilla/show_bug.cgi?id=12275)(2010-)

Systemtap
packagemain
import(
"bytes"
"fmt"
"math/rand"
"time"
)
funcToString(numberint)string{
returnfmt.Sprintf("%d",number)
}
funcmain(){
r:=rand.New(rand.NewSource(time.Now().UnixNano()))
varbufbytes.Buffer
fori:=0;i<1000;i++{
value:=r.Int()%1000
value=value-500
buf.WriteString(ToString(value))
}
}

Systemtap
globalintervals
probeprocess("systemtap02").function("main.ToString").call {
intervals<<<$number
}
probeend{
printf("Variablesmin:%dusavg:%dusmax:%duscount:%dn",
@min(intervals),@avg(intervals),@max(intervals),
@count(intervals))
printf("Variables:n")
print(@hist_log(intervals));
printf("n")
}

Systemtap
Variablesmin:-499usavg:8usmax:497uscount:1000
Variables:
value|--------------------------------------------------count
-256|@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 249
-128|@@@@@@@@@@@@@@@@@@@@ 121
-64|@@@@@@@@@@ 60
-32|@@@@@@ 36
-16|@@ 12
-8|@ 8
-4| 5
-2| 3
-1| 2
0| 2
1| 2
2| 3
4|@ 7
8| 4
16|@@@ 20
32|@@@@@ 33
64|@@@@@@@ 44
128|@@@@@@@@@@@@@@@@@@ 110
256|@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 279

perf and perf_events
$sudoperftop-p$(pidofsystemtap)

perf and perf_events

Brendan Gregg Flame Graphs
www.brendangregg.com/ amegraphs.html(http://www.brendangregg.com/ amegraphs.html)
Systems Performance: Enterprise and the Cloud
goo.gl/556Hs2(http://goo.gl/556Hs2)
$sudoperfrecord-F99-g-p$(pidofsystemtap)--sleep10
[perfrecord:Wokenup1timestowritedata]
[perfrecord:Capturedandwrote0.149MBperf.data(1719samples)]
$sudoperfscript|~/tmp/FlameGraph/stackcollapse-perf.pl>out.perf-folded
$~/tmp/FlameGraph/flamegraph.plout.perf-folded>perf-kernel.svg

Brendan Gregg Flame Graphs
Kernel stack traces!

Memory
What if we were in C/C++ world? Valgrind! Massif!
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
intmain(){
constsize_tMB=1024*1024;
constunsignedcount=20;
char**buf=calloc(count,sizeof(*buf));
for(unsignedi=0;i<count;i++){
buf[i]=calloc(1,MB);
memset(buf[i],0xFF,MB);
sleep(1);
}
for(unsignedi=0;i<count;i++){
free(buf[i]);
sleep(1);
}
free(buf);
}

Vagrind and Massif
26.20^ ::
| :::#
| @@::#::
| ::@::#:::
| :::::@::#::::::
| ::::@::#::::::
| ::::::@::#::::::
| :::::::::@::#::::::::::
| :::::::::@::#::::::::@@
| ::::::::::@::#::::::::@::
| ::@:::::::::@::#::::::::@::::
| :::@:::::::::@::#::::::::@:::::
| ::::@:::::::::@::#::::::::@::::::
| :::::@:::::::::@::#::::::::@:::::::
|::::::::@:::::::::@::#::::::::@::::::::::
|:::::::@:::::::::@::#::::::::@:::::::::
|@::::::@:::::::::@::#::::::::@:::::::::@
|@::::::@:::::::::@::#::::::::@:::::::::@
|@::::::@:::::::::@::#::::::::@:::::::::@
|@::::::@:::::::::@::#::::::::@:::::::::@
0+----------------------------------------------------------------------->s
0 39.13

Valgrind and Massif
Valgrind rede nes all memory allocation functions (malloc, calloc, new, free, etc.).
Go do not use them. Go has their own memory allocator which uses mmap or sbrk.

Memory
Valgrind can catch mmap/sbrk, but there is no point.
All other memory pro ling tools work in the same fashion.
We can theoretically use perf/systemtap
Or we can use rich internal tools

Memory
Go can collect information about allocations with some rate (once in 512KiB by
default).
pprof can visualize it.
Similar to CPU pro ling, we have three ways to collect data. Let's use net/http/pprof
this time.

Example
import_"net/http/pprof"
funcallocAndKeep(){
varb[][]byte
for{
b=append(b,make([]byte,1024))
time.Sleep(time.Millisecond)
}
}
funcallocAndLeave(){
varb[][]byte
for{
b=append(b,make([]byte,1024))
iflen(b)==20{
b=nil
}
time.Sleep(time.Millisecond)
}
}
funcmain(){
goallocAndKeep()
goallocAndLeave()
http.ListenAndServe("0.0.0.0:8080",nil)
}

go tool pprof
alloc_space - allocated bytes
alloc_objects - number of allocated objects
inuse_space - allocated bytes that are in use (live)
inuse_objects - number of allocated objects that are in use (live)
We expect inuse to show only allocAndKeep() and alloc to show both functions.

go tool pprof
$gotoolpprof-inuse_spacememtesthttp://localhost:8080/debug/pprof/heap
Fetchingprofilefromhttp://localhost:8080/debug/pprof/heap
Savedprofilein/home/marko/pprof/pprof.memtest.localhost:8080.inuse_objects.inuse_space.005.pb.gz
Enteringinteractivemode(type"help"forcommands)
(pprof)top
15.36MBof15.36MBtotal( 100%)
Dropped2nodes(cum<=0.08MB)
15.36MB 100% 100% 15.36MB 100% main.allocAndKeep
0 0% 100% 15.36MB 100% runtime.goexit
$gotoolpprof-alloc_spacememtesthttp://localhost:8080/debug/pprof/heap
Fetchingprofilefromhttp://localhost:8080/debug/pprof/heap
Savedprofilein/home/marko/pprof/pprof.memtest.localhost:8080.alloc_objects.alloc_space.008.pb.gz
Enteringinteractivemode(type"help"forcommands)
(pprof)top
54.49MBof54.49MBtotal( 100%)
27.97MB51.33%51.33% 29.47MB54.08% main.allocAndKeep
23.52MB43.17%94.49% 25.02MB45.92% main.allocAndLeave
3MB 5.51% 100% 3MB 5.51% time.Sleep
0 0% 100% 54.49MB 100% runtime.goexit

Sleep?
Looks like predicted. But what is with sleep?
(pprof)listtime.Sleep
Total:54.49MB
ROUTINE========================time.Sleepin/home/marko/go/src/runtime/time.go
3MB 3MB(flat,cum) 5.51%ofTotal
. . 48:functimeSleep(nsint64){
. . 49: ifns<=0{
. . 50: return
. . 51: }
. . 52:
3MB 3MB 53: t:=new(timer)
. . 54: t.when=nanotime()+ns
. . 55: t.f=goroutineReady
. . 56: t.arg=getg()
. . 57: lock(&timers.lock)
. . 58: addtimerLocked(t)

Implicit allocations
packageprinttest
import(
"bytes"
"fmt"
"testing"
)
funcBenchmarkPrint(b*testing.B){
varbufbytes.Buffer
varsstring="teststring"
fori:=0;i<b.N;i++{
buf.Reset()
fmt.Fprintf(&buf,"stringis:%s",s)
}
}
Benchmark?

Benchmark
$gotest-bench=.-benchmem
BenchmarkPrint-8 10000000 128ns/op 16B/op 1allocs/op
PASS
ok github.com/mkevac/converttest 1.420s

Pro ling
$gotest-bench=.-memprofile=mem.out-memprofilerate=1
mempro lerate sets pro ling rate. 1 means all allocations.
$ go tool pprof -alloc_space converttest.test mem.out
(pprof)top
15.41MBof15.48MBtotal(99.59%)
15.41MB99.59%99.59% 15.43MB99.67% github.com/mkevac/converttest.BenchmarkPrint
0 0%99.59% 15.47MB99.93% runtime.goexit
0 0%99.59% 15.42MB99.66% testing.(*B).launch
0 0%99.59% 15.43MB99.67% testing.(*B).runN

Pro ling
(pprof)listBenchmarkPrint
Total:15.48MB
ROUTINE========================github.com/mkevac/converttest.BenchmarkPrintin/home/marko/goproject
15.41MB 15.43MB(flat,cum)99.67%ofTotal
. . 9:funcBenchmarkPrint(b*testing.B){
. . 10: varbufbytes.Buffer
. . 11: varsstring="teststring"
. . 12: fori:=0;i<b.N;i++{
. . 13: buf.Reset()
15.41MB 15.43MB 14: fmt.Fprintf(&buf,"stringis:%s",s)
. . 15: }
. . 16:}

Pro ling
(pprof)listfmt.Fprintf
Total:15.48MB
ROUTINE========================fmt.Fprintfin/home/marko/go/src/fmt/print.go
0 12.02kB(flat,cum)0.076%ofTotal
. . 175://Theseroutinesendin'f'andtakeaformatstring.
. . 176:
. . 177://Fprintfformatsaccordingtoaformatspecifierandwritestow.
. . 178://Itreturnsthenumberofbyteswrittenandanywriteerrorencountered.
. . 179:funcFprintf(wio.Writer,formatstring,a...interface{})(nint,errerror)
. 11.55kB 180: p:=newPrinter()
. 480B 181: p.doPrintf(format,a)
. . 182: n,err=w.Write(p.buf)
. . 183: p.free()
. . 184: return
. . 185:}
. . 186:

Disassembly
. . 466edb:CALLbytes.(*Buffer).Reset(SB)
. . 466ee0:LEAQ0x98b6b(IP),AX
. . 466ee7:MOVQAX,0x70(SP)
. . 466eec:MOVQ$0xb,0x78(SP)
. . 466ef5:MOVQ$0x0,0x60(SP)
. . 466efe:MOVQ$0x0,0x68(SP)
. . 466f07:LEAQ0x70d92(IP),AX
. . 466f0e:MOVQAX,0(SP)
. . 466f12:LEAQ0x70(SP),AX
. . 466f17:MOVQAX,0x8(SP)
. . 466f1c:MOVQ$0x0,0x10(SP)
15.41MB 15.41MB 466f25:CALLruntime.convT2E(SB)
. . 466f2a:MOVQ0x18(SP),AX
. . 466f2f:MOVQ0x20(SP),CX
. . 466f34:MOVQAX,0x60(SP)
. . 466f39:MOVQCX,0x68(SP)
. . 466f3e:LEAQ0x10b35b(IP),AX
. . 466f45:MOVQAX,0(SP)
. . 466f49:MOVQ0x58(SP),AX
. . 466f4e:MOVQAX,0x8(SP)
. . 466f53:LEAQ0x99046(IP),CX
. . 466f5a:MOVQCX,0x10(SP)

. . 466f5f:MOVQ$0xd,0x18(SP)
. . 466f68:LEAQ0x60(SP),CX
. . 466f6d:MOVQCX,0x20(SP)
. . 466f72:MOVQ$0x1,0x28(SP)
. . 466f7b:MOVQ$0x1,0x30(SP)
. 12.02kB 466f84:CALLfmt.Fprintf(SB)

fprintf
funcFprintf(wio.Writer,formatstring,a...interface{})(nint,errerror)
interface{} same as void*... but it's not

Go internal types
string, chan, func, slice, interface, etc.

Empty interface
varsstring=“marko”
varainterface{}=&s
no allocation
varsstring=“marko”
varainterface{}=s
16 bytes allocation

Empty interface

Fix
packagemain
import(
"bytes"
"testing"
)
funcBenchmarkPrint(b*testing.B){
varbufbytes.Buffer
varsstring="teststring"
fori:=0;i<b.N;i++{
buf.Reset()
buf.WriteString("stringis:")
buf.WriteString(s)
}
}
Benchmark?

Benchmark
$gotest-bench=BenchmarkPrint-benchmem
BenchmarkPrint-8 50000000 27.5ns/op 0B/op 0allocs/op
PASS
ok github.com/mkevac/converttest01 1.413s
0 allocations and 4x speed

Implicit allocation
String and char * pretty much the same in C. But not in Go.
packagemain
import(
"fmt"
)
funcmain(){
vararray=[]byte{'m','a','r','k','o'}
ifstring(array)=="marko"{
fmt.Println("equal")
}
}

Implicit allocation
Always check your assumptions.
Go runtime, Go compiler and Go tools are better with each day.
Some optimization you read about in 2010 could be not needed. Or can be harmful.

Example (again)
packagemain
import(
"bytes"
"testing"
"unsafe"
)
varsstring
funcBenchmarkConvert(b*testing.B){
varbufbytes.Buffer
vararray=[]byte{'m','a','r','k','o',0}
fori:=0;i<b.N;i++{
buf.Reset()
s=string(array)
buf.WriteString(s)
}
}

Benchmark
BenchmarkConvert-8 30000000 42.1ns/op 8B/op 1allocs/op

Fix
funcBytesToString(b[]byte)string{
bh:=(*reflect.SliceHeader)(unsafe.Pointer(&b))
sh:=reflect.StringHeader{bh.Data,bh.Len}
return*(*string)(unsafe.Pointer(&sh))
}
funcBenchmarkNoConvert(b*testing.B){
varbufbytes.Buffer
vararray=[]byte{'m','a','r','k','o',0}
fori:=0;i<b.N;i++{
buf.Reset()
s=BytesToString(array)
buf.WriteString(s)
}
}

Benchmark
BenchmarkConvert-8 30000000 44.5ns/op 8B/op 1allocs/op
BenchmarkNoConvert-8 100000000 19.2ns/op 0B/op 0allocs/op
PASS
ok github.com/mkevac/bytetostring 3.332s

Tracing
Go runtime writes almost everything it does.
Scheduling, channel operations, locks, thread creation, ...
Full list in runtime/trace.go
For visualization go tool trace uses same JS package that Chrome uses for page loading
visualization.
Example.

debugcharts
github.com/mkevac/debugcharts(http://github.com/mkevac/debugcharts)
runtime.ReadMemStats() once a second

Example
import(
"net/http"
_"net/http/pprof"
"time"
_"github.com/mkevac/debugcharts"
)
funcCPUHogger(){
varaccuint64
t:=time.Tick(2*time.Second)
for{
select{
case<-t:
time.Sleep(50*time.Millisecond)
default:
acc++
}
}
}
funcmain(){
goCPUHogger()
goCPUHogger()
http.ListenAndServe("0.0.0.0:8181",nil)
}

Tracing
$curlhttp://localhost:8181/debug/pprof/trace?seconds=10-otrace.out
Sometimes all you can visualize is 1-3 seconds.
$gotooltrace-http"0.0.0.0:8080"./tracetesttrace.out

Tracing

proc stop and proc start

runtime.ReadMemStats()
180//ReadMemStatspopulatesmwithmemoryallocatorstatistics.
181funcReadMemStats(m*MemStats){
182 stopTheWorld("readmemstats")
183
184 systemstack(func(){
185 readmemstats_m(m)
186 })
187
188 startTheWorld()
189}
Production? No!

Conclusion
There are so much more

Conlusion
CPU pro ler
Memory pro ler
All allocations tracing
Escape analysis
Lock/Contention pro ler
Scheduler tracing
Tracing
GC tracing
Real time memory statistics
System pro lers like perf and systemtap.
But no tool will replace deep understanding of how your program works from start to
nish.

I hope that today's crash course was helpful.

Stay curious

Thank you
Marko Kevac
Software Engineer, Badoo
marko@kevac.org(mailto:marko@kevac.org)
@mkevac(http://twitter.com/mkevac)

Profiling and optimizing go programs

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