Duplicate and unnecessary system call in pkg/kernel/GetVersionInfo()

[eryx]

Ⅰ. Issue Description

as the image (perf record to flame graph) below, i found a CPU hot point in the pkg/kernel/GetVersionInfo().

this method may only need to be called once, because the kernel version is fixed after the system is up. ?

Ⅱ. Describe what happened

Ⅲ. Describe what you expected to happen

Ⅳ. How to reproduce it (as minimally and precisely as possible)

Ⅴ. Anything else we need to know?

Ⅵ. Environment:

• pouch version (use pouch version): 1.0.0
• OS (e.g. from /etc/os-release): CentOS 7.x
• Kernel (e.g. uname -a):
• Install tools: rpm -ivh
• Others:

[houstar]

Good idea, you may assume that kernel version is fixed for most cases, but for kexec? Since kexec can be dynamically switch the kernel version :-)

[eryx]

@houstar
yes, the kexec will cause problems

[houstar]

This is trade-off problem 👍 Let's the architects make the decision. If plan to merge, add this kexec problem as Limitation 💯

[HusterWan]

Great point, I even not think about kexec at all. 🤣

But, IMO, the kexec is not a problem, right now. We may first think about fix the hot point of pouchd, then care about the kexec problem. WDYT? @eryx @houstar

[houstar]

I'm totally agree with you @HusterWan since this is trade-off problem and add kexec as limitation.

[zhuangqh]

have you compare it with syscall.Uname?

package main

import (
	"fmt"
	"syscall"
)

func main() {
	err := syscall.Uname(&buf)
	if err != nil {
		fmt.Println(err)
		return
	}

	fmt.Println(charsToString(buf.Release[:]))
}

func charsToString(ca []int8) string {
	s := make([]byte, len(ca))
	var lens int
	for ; lens < len(ca); lens++ {
		if ca[lens] == 0 {
			break
		}
		s[lens] = uint8(ca[lens])
	}
	return string(s[0:lens])
}

$ root@pouch:~/go/src/github.com/t# go build main.go
$ root@pouch:~/go/src/github.com/t# ./main
4.4.0-137-generic

What's the performance of this one?

[SimonCqk]

@zhuangqh I've just tried a simple test, use unix.Uname instead of syscall.Uname, comparing with exec.Run version, and the result shows that the performance difference can't be omitted.
Call 1000 times in one loop:
exec.Run takes 3.3s while unix.Uname takes 8.5ms (in mean)

[SimonCqk]

@zhuangqh here is my code:

func GetKernelVersionByUnix() (*VersionInfo, error) {
	var (
		kernel, major, minor int
		flavor               string
	)
	buf := unix.Utsname{}
	err := unix.Uname(&buf)
	if err != nil {
		return nil, err
	}
	release := string(buf.Release[:])
	parsed, _ := fmt.Sscanf(release, "%d.%d.%d-%s", &kernel, &major, &minor, &flavor)
	if parsed < 3 {
		return nil, fmt.Errorf("Can't parse kernel version, release: %s" + release)
	}

	return &VersionInfo{
		Kernel: kernel,
		Major:  major,
		Minor:  minor,
		Flavor: flavor,
	}, nil
}

[zhuangqh]

@zhuangqh here is my code:

func GetKernelVersionByUnix() (*VersionInfo, error) {
	var (
		kernel, major, minor int
		flavor               string
	)
	buf := unix.Utsname{}
	err := unix.Uname(&buf)
	if err != nil {
		return nil, err
	}
	release := string(buf.Release[:])
	parsed, _ := fmt.Sscanf(release, "%d.%d.%d-%s", &kernel, &major, &minor, &flavor)
	if parsed < 3 {
		return nil, fmt.Errorf("Can't parse kernel version, release: %s" + release)
	}

	return &VersionInfo{
		Kernel: kernel,
		Major:  major,
		Minor:  minor,
		Flavor: flavor,
	}, nil
}

good job! Could you submit a pull request?

[eryx]

bench in multi-implementation

=== RUN TestGetKernelVersion
3.10.0-862.14.4.el7.x86_64
--- PASS: TestGetKernelVersion (0.00s)
goos: linux
goarch: amd64
pkg: github.com/alibaba/pouch/pkg/kernel
Benchmark_GetKernelVersion-8 3000 550459 ns/op
Benchmark_GetKernelVersionByVarCache-8 2000000000 1.78 ns/op
Benchmark_GetKernelVersionByVarCacheWithTTL-8 50000000 39.8 ns/op
Benchmark_GetKernelVersionByUnix-8 500000 3258 ns/op
Benchmark_GetKernelVersionBySyscall-8 1000000 2279 ns/op
PASS
ok github.com/alibaba/pouch/pkg/kernel 11.459s

Codes:
https://github.com/eryx/pouch/blob/kernel-version-bench/pkg/kernel/kernel.go
https://github.com/eryx/pouch/blob/kernel-version-bench/pkg/kernel/kernel_test.go