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sysfs: enable overriding CPU cache configuration from env
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If OVERRIDE_SYS_CACHES environment variable is defined, discovering
CPU cache configuration from sysfs is skipped and the configuration is
parsed from the json in the variable instead.

Signed-off-by: Antti Kervinen <[email protected]>
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askervin committed Oct 17, 2024
1 parent 3c1a1b7 commit adce006
Showing 1 changed file with 139 additions and 11 deletions.
150 changes: 139 additions & 11 deletions pkg/sysfs/system.go
Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
package sysfs

import (
"encoding/json"
"errors"
"fmt"
"io/fs"
Expand Down Expand Up @@ -277,6 +278,8 @@ var (
PerformanceCore: "OVERRIDE_SYS_CORE_CPUS",
EfficientCore: "OVERRIDE_SYS_ATOM_CPUS",
}
cacheEnvOverridesVar = "OVERRIDE_SYS_CACHES"
cacheEnvOverridesJson = os.Getenv(cacheEnvOverridesVar)
)

// MemInfo contains data read from a NUMA node meminfo file.
Expand Down Expand Up @@ -306,6 +309,21 @@ type Cache struct {
cpus idset.IDSet // CPUs sharing this cache
}

// cacheOverrides is a list of cache overrides for specific CPU sets.
// Every CPU set gets cache id that starts from 0 on each override object.
// Example: two 128 MB L3 Caches shared by CPUs 0-15,32-47 (socket 0)
// and 16-31,48-63 (socket 1). The cache id is 0 for the first, 1 for the second.
// [{"cpusets": ["0-15,32-47", "16-31,48-63"], "level": 3, "size": "128M"}]
type cacheOverrides []cacheOverride
type cacheOverride struct {
Cpusets []string // cpusets to which this override applies
Level int // cache level
Kind string // "d" for data, "i" for instruction, "u" for unified
Size string // cache size, e.g. "4M"
}

var cacheEnvOverrides map[int][]*Cache

// SetSysRoot sets the sys root directory.
func SetSysRoot(root string) {
if root != "" {
Expand Down Expand Up @@ -934,17 +952,24 @@ func (sys *system) discoverCPU(path string) error {
}

if (sys.flags & DiscoverCache) != 0 {
entries, _ := filepath.Glob(filepath.Join(path, "cache/index[0-9]*"))
slices.SortFunc(entries, func(a, b string) int {
a = strings.TrimPrefix(filepath.Base(a), "index")
b = strings.TrimPrefix(filepath.Base(b), "index")
idxA, _ := strconv.Atoi(a)
idxB, _ := strconv.Atoi(b)
return idxA - idxB
})
for _, entry := range entries {
if err := sys.discoverCache(cpu, entry); err != nil {
return err
overridden, err := sys.discoverCacheFromOverrides(cpu)
if err != nil {
return err
}
if !overridden {
// discover caches for this CPU from sysfs
entries, _ := filepath.Glob(filepath.Join(path, "cache/index[0-9]*"))
slices.SortFunc(entries, func(a, b string) int {
a = strings.TrimPrefix(filepath.Base(a), "index")
b = strings.TrimPrefix(filepath.Base(b), "index")
idxA, _ := strconv.Atoi(a)
idxB, _ := strconv.Atoi(b)
return idxA - idxB
})
for _, entry := range entries {
if err := sys.discoverCache(cpu, entry); err != nil {
return err
}
}
}
}
Expand Down Expand Up @@ -1526,6 +1551,84 @@ func (sys *system) discoverSst() error {
return nil
}

func parseSize(s string) (uint64, error) {
var size uint64
var unit string
if _, err := fmt.Sscanf(s, "%d%s", &size, &unit); err != nil {
if _, err := fmt.Sscanf(s, "%d", &size); err != nil {
return 0, err
}
}
switch unit {
case "k", "K", "KB":
size *= 1 << 10
case "M", "MB":
size *= 1 << 20
case "G", "GB":
size *= 1 << 30
case "T", "TB":
size *= 1 << 40
case "":
default:
return 0, fmt.Errorf("unknown unit %q", unit)
}
return size, nil
}

// Parse cache overrides from a JSON string.
func parseCpuCacheOverrides(overrideJson string) (map[int][]*Cache, error) {
cpuCacheOverrides := make(map[int][]*Cache)
if overrideJson == "" {
return cpuCacheOverrides, nil
}
parseCcoError := func(format string, args ...interface{}) error {
return fmt.Errorf("cache override: "+format, args...)
}
overrides := cacheOverrides{}
if err := json.Unmarshal([]byte(overrideJson), &overrides); err != nil {
return nil, parseCcoError("unmarshaling %q failed: %v", overrideJson, err)
}
for _, override := range overrides {
nextId := 0
for _, cpusetStr := range override.Cpusets {
cpusCpuset, err := cpuset.Parse(cpusetStr)
if err != nil {
return nil, parseCcoError("parsing cpuset %q failed: %v\n", cpusetStr, err)
}
cpus := idset.NewIDSet(cpusCpuset.UnsortedList()...)
c := &Cache{
id: idset.ID(nextId),
}
nextId++
switch strings.ToLower(override.Kind) {
case "d", "data":
c.kind = DataCache
case "i", "instruction":
c.kind = InstructionCache
case "u", "unified", "":
c.kind = UnifiedCache
default:
return nil, parseCcoError("unknown cache kind %q\n", override.Kind)
}
if override.Level > 0 {
c.level = override.Level
} else {
c.level = 1
}
c.size, err = parseSize(override.Size)
if err != nil {
return nil, parseCcoError("parsing size %q failed: %v\n", override.Size, err)
}
c.cpus = cpus
for _, cpu := range cpus.Members() {
cpuCacheOverrides[cpu] = append(cpuCacheOverrides[cpu], c)
}
log.Debugf("override cache: %+v", *c)
}
}
return cpuCacheOverrides, nil
}

// ID returns the id of this package.
func (p *cpuPackage) ID() idset.ID {
return p.id
Expand Down Expand Up @@ -1610,6 +1713,31 @@ func (p *cpuPackage) SstInfo() *sst.SstPackageInfo {
return p.sstInfo
}

// Discover cache from overrides returns true if caches for a cpu were discovered.
func (sys *system) discoverCacheFromOverrides(cpu *cpu) (bool, error) {
if cacheEnvOverridesJson == "" {
return false, nil
}
if cacheEnvOverrides == nil {
sys.Debug("parsing cache overrides from %s=%q", cacheEnvOverridesVar, cacheEnvOverridesJson)
ceo, err := parseCpuCacheOverrides(cacheEnvOverridesJson)
if err != nil {
sys.Error("failed to parse cache overrides: %v", err)
return false, err
}
cacheEnvOverrides = ceo
}
if caches, ok := cacheEnvOverrides[cpu.id]; ok {
cpu.caches = make([]*Cache, len(caches))
for i, c := range caches {
sys.Debug("cpu %d cache override %+v", cpu.id, *c)
cpu.caches[i] = sys.saveCache(c)
}
return true, nil
}
return false, nil
}

// Discover cache associated with the given CPU.
func (sys *system) discoverCache(cpu *cpu, path string) error {
var id idset.ID
Expand Down

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