mirror of
https://github.com/token2/snapd.git
synced 2026-03-13 11:15:47 -07:00
bf067f57db
Ideas employed
- reorder fields so that mask is before the string
- use POPCNT to estimate allocation size
- allocate late on demand
- pre-compute mask of known flags
- bail out when known flags are handled
This yields improvements in most of the benchmarks:
Before:
BenchmarkUnmountFlagsToOptsAllMissing-4 200000000 6.07 ns/op
BenchmarkUnmountFlagsToOptsMixed-4 50000000 36.8 ns/op
BenchmarkUnmountFlagsToOptsAllPresent-4 10000000 158 ns/op
BenchmarkMountFlagsToOptsAllMissing-4 200000000 9.93 ns/op
BenchmarkMountFlagsToOptsAllPresent-4 10000000 230 ns/op
BenchmarkMountFlagsToOptsMixed-4 30000000 41.4 ns/op
BenchmarkMountFlagsToOptsTypical-4 30000000 41.8 ns/op
After:
BenchmarkUnmountFlagsToOptsAllMissing-4 500000000 3.41 ns/op
BenchmarkUnmountFlagsToOptsMixed-4 30000000 54.3 ns/op
BenchmarkUnmountFlagsToOptsAllPresent-4 20000000 63.8 ns/op
BenchmarkMountFlagsToOptsAllMissing-4 500000000 3.71 ns/op
BenchmarkMountFlagsToOptsAllPresent-4 20000000 83.6 ns/op
BenchmarkMountFlagsToOptsMixed-4 20000000 51.5 ns/op
BenchmarkMountFlagsToOptsTypical-4 50000000 33.2 ns/op
I've also added a "typical" benchmark with one known flag only.
Signed-off-by: Zygmunt Krynicki <me@zygoon.pl>
91 lines
2.4 KiB
Go
91 lines
2.4 KiB
Go
// -*- Mode: Go; indent-tabs-mode: t -*-
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/*
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* Copyright (C) 2019 Canonical Ltd
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 3 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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package mount
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import (
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"math/bits"
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"syscall"
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)
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type flagInfo struct {
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mask uint32
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name string
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}
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func knownMask(knownFlags []flagInfo) uint32 {
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var mask uint32
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for _, fi := range knownFlags {
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mask |= fi.mask
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}
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return mask
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}
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// UMOUNT_NOFOLLOW is not defined in go's syscall package
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const UMOUNT_NOFOLLOW = 8
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var mountFlags = []flagInfo{
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{name: "MS_REMOUNT", mask: syscall.MS_REMOUNT},
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{name: "MS_BIND", mask: syscall.MS_BIND},
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{name: "MS_REC", mask: syscall.MS_REC},
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{name: "MS_RDONLY", mask: syscall.MS_RDONLY},
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{name: "MS_SHARED", mask: syscall.MS_SHARED},
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{name: "MS_SLAVE", mask: syscall.MS_SLAVE},
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{name: "MS_PRIVATE", mask: syscall.MS_PRIVATE},
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{name: "MS_UNBINDABLE", mask: syscall.MS_UNBINDABLE},
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}
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var mountFlagsMask = knownMask(mountFlags)
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var unmountFlags = []flagInfo{
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{name: "UMOUNT_NOFOLLOW", mask: UMOUNT_NOFOLLOW},
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{name: "MNT_FORCE", mask: syscall.MNT_FORCE},
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{name: "MNT_DETACH", mask: syscall.MNT_DETACH},
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{name: "MNT_EXPIRE", mask: syscall.MNT_EXPIRE},
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}
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var unmountFlagsMask = knownMask(unmountFlags)
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func flagOptSearch(flags int, knownFlags []flagInfo, knownMask uint32) (opts []string, unknown int) {
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var f uint32 = uint32(flags)
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for _, fi := range knownFlags {
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if f&knownMask == 0 {
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break
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}
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if f&fi.mask != 0 {
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if opts == nil {
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opts = make([]string, 0, bits.OnesCount32(f))
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}
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f ^= fi.mask
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opts = append(opts, fi.name)
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}
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}
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return opts, int(f)
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}
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// MountFlagsToOpts returns the symbolic representation of mount flags.
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func MountFlagsToOpts(flags int) (opts []string, unknown int) {
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return flagOptSearch(flags, mountFlags, mountFlagsMask)
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}
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// UnmountFlagsToOpts returns the symbolic representation of unmount flags.
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func UnmountFlagsToOpts(flags int) (opts []string, unknown int) {
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return flagOptSearch(flags, unmountFlags, unmountFlagsMask)
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}
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