wip.slide

* Misc notes: ASM/Cgo

- [[https://golang.org/doc/asm]]
- [[http://goroutines.com/asm]]

Cgo - call C functions from Go:

- Per call overhead ~150ns. or use gccgo, but generated go code by gccgo may not be as good as the native compiler.
- This is changing all the time.

- [[http://jmoiron.net/blog/go-performance-tales]] (old'ish)

* Misc notes: Memory

memprofile

- default, what's held onto now
- -alloc_objects, what's doing allocs
- go tool pprof -alloc_objects (binary) (pprof output)

mallocgc is the function which allocates memory in Go

- if it shows up too often it's time to see why you're allocating

* Misc notes: Strings

- HasPrefix - just check it if it's a single char.
- Split, Trim, regexp
- table optimization (character -> int output)
- Don't read a string if you don't have to, use the bytes. allocs to do conversions, runes for utf8.
- don't use + concatenation, bytes.Buffer WriteString
- runtime.convT2E - convert type to empty interface, seen in disasm
- strings won't fit in the 2 word space for an empty interface

* Misc notes: Pools, profiling

sync.Pool:

- bytes.ByteBuffer

Contention profiling:

- go test -bench=. -blockprofile=prof.block

Reading a file:

- bufio.NewReader, writing: bytes.Buffer

syscalls:

- os.hostname

defer has a cost

go tool pprof -seconds 5 http://localhost:9090/debug/pprof/profile

sync/atomic - 100's of cores (256 cores) synchronization takes time.

go-torch -u http://localhost:9090 --time 5
go-torch --binary-name foo.test.exe -b cpu.out
go test -run=none -bench . -benchmem -cpuprofile cpu.out -memprofile prof.mem
branch prediction
locality

pprof, can filter graph to calls which took more than x% of time

profiling has to run long enough, it does sample (once per 100 cycles??)

"free lists" vs sync.Pool

https://github.com/cloudflare/golibs
- bytepool
- lrucache
- circularbuffer

https://github.com/facebookgo

benchstat

Slow leaks, in prod:
import _ "net/http/pprof"
cpu, memory, contention

regexp has free lists + mutex

Prometheus - visualization for instrumentation

gcflags = not "garbage collector", "go compiler flags"

Memory alignment - avoid wasted bytes for padding)

defer without "func()" evaluates closures immediate; if ptr reassigned it retains the old pointer value

http://blog.rocana.com/golang-escape-analysis

Go Escape Analysis Flaws Dmitry Vyukov, @dvyukov Feb 10, 2015
https://docs.google.com/document/d/1CxgUBPlx9iJzkz9JWkb6tIpTe5q32QDmz8l0BouG0Cw/preview

http://www.florinpatan.ro/2016/05/visualizing-profiling-in-go-different.html