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reduce CPU usage running large numbers of clients #5951

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merged 6 commits into from
Jul 19, 2019
Merged

reduce CPU usage running large numbers of clients #5951

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412997f
pid_collector getAllPids -> getAllPidsByScanning
langmartin Jul 17, 2019
d3ef456
resource_container_linux new getAllPidsByCgroup
langmartin Jul 9, 2019
3834616
executor use e.getAllPids()
langmartin Jul 9, 2019
1a9c598
executor_universal_linux getAllPids chooses cgroup when available
langmartin Jul 10, 2019
ab3e625
executor_unix and _windows stub getAllPids ByScanning
langmartin Jul 17, 2019
7bd881c
default e.getAllPids in executor_basic
langmartin Jul 18, 2019
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2 changes: 1 addition & 1 deletion drivers/shared/executor/executor.go
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Original file line number Diff line number Diff line change
Expand Up @@ -312,7 +312,7 @@ func (e *UniversalExecutor) Launch(command *ExecCommand) (*ProcessState, error)
return nil, fmt.Errorf("failed to start command path=%q --- args=%q: %v", path, e.childCmd.Args, err)
}

go e.pidCollector.collectPids(e.processExited, getAllPids)
go e.pidCollector.collectPids(e.processExited, e.getAllPids)
go e.wait()
return &ProcessState{Pid: e.childCmd.Process.Pid, ExitCode: -1, Time: time.Now()}, nil
}
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4 changes: 4 additions & 0 deletions drivers/shared/executor/executor_basic.go
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Expand Up @@ -15,3 +15,7 @@ func NewExecutorWithIsolation(logger hclog.Logger) Executor {
func (e *UniversalExecutor) configureResourceContainer(_ int) error { return nil }

func (e *UniversalExecutor) runAs(_ string) error { return nil }

func (e *UniversalExecutor) getAllPids() (map[int]*nomadPid, error) {
return getAllPidsByScanning()
}
15 changes: 14 additions & 1 deletion drivers/shared/executor/executor_universal_linux.go
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Expand Up @@ -75,11 +75,24 @@ func (e *UniversalExecutor) configureResourceContainer(pid int) error {
},
}

configureBasicCgroups(cfg)
err := configureBasicCgroups(cfg)
if err != nil {
e.logger.Warn("failed to create cgroup", "error", err)
return err
}

e.resConCtx.groups = cfg.Cgroups
return cgroups.EnterPid(cfg.Cgroups.Paths, pid)
}

func (e *UniversalExecutor) getAllPids() (map[int]*nomadPid, error) {
if e.resConCtx.isEmpty() {
return getAllPidsByScanning()
} else {
return e.resConCtx.getAllPidsByCgroup()
}
}

// DestroyCgroup kills all processes in the cgroup and removes the cgroup
// configuration from the host. This function is idempotent.
func DestroyCgroup(groups *lconfigs.Cgroup, executorPid int) error {
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2 changes: 1 addition & 1 deletion drivers/shared/executor/pid_collector.go
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Expand Up @@ -210,7 +210,7 @@ func aggregatedResourceUsage(systemCpuStats *stats.CpuStats, pidStats map[string
}
}

func getAllPids() (map[int]*nomadPid, error) {
func getAllPidsByScanning() (map[int]*nomadPid, error) {
allProcesses, err := ps.Processes()
if err != nil {
return nil, err
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37 changes: 37 additions & 0 deletions drivers/shared/executor/resource_container_linux.go
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Expand Up @@ -4,6 +4,8 @@ import (
"os"
"sync"

"github.com/hashicorp/nomad/client/stats"
"github.com/opencontainers/runc/libcontainer/cgroups"
cgroupConfig "github.com/opencontainers/runc/libcontainer/configs"
)

Expand All @@ -23,3 +25,38 @@ func (rc *resourceContainerContext) executorCleanup() error {
}
return nil
}

func (rc *resourceContainerContext) isEmpty() bool {
return rc.groups == nil
}

func (rc *resourceContainerContext) getAllPidsByCgroup() (map[int]*nomadPid, error) {
nPids := map[int]*nomadPid{}

if rc.groups == nil {
return nPids, nil
}

var path string
if p, ok := rc.groups.Paths["freezer"]; ok {
path = p
} else {
path = rc.groups.Path
}
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For cgroups, we want to use a single cgroup hierarchy. Checking multiple hierarchy would lead to duplicate values in the case of multiple cgroups attached.

In Nomad, we always create the freezer cgroup only in configureBasicCgroups[1], so that's an appropriate one to use. For comparison, docker/runc requires devices cgroup to be mounted, so they only check the devices subsystem[2]

[1]

nomad/drivers/shared/executor/executor_linux.go

Lines 715 to 728 in 88c03d0

// Manually create freezer cgroup
cfg.Cgroups.Paths = map[string]string{}
root, err := cgroups.FindCgroupMountpointDir()
if err != nil {
return err
}
if _, err := os.Stat(root); err != nil {
return err
}
freezer := cgroupFs.FreezerGroup{}
subsystem := freezer.Name()
path, err := cgroups.FindCgroupMountpoint("", subsystem)

[2] https://github.com/opencontainers/runc/blob/master/libcontainer/cgroups/fs/apply_raw.go#L286-L289

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in configureBasicCgroups, we make an empty Freezer and ask it it's name, which constantly returns "freezer". Should I do that here? or use just the string over there?


pids, err := cgroups.GetAllPids(path)
if err != nil {
return nPids, err
}

for _, pid := range pids {
nPids[pid] = &nomadPid{
pid: pid,
cpuStatsTotal: stats.NewCpuStats(),
cpuStatsUser: stats.NewCpuStats(),
cpuStatsSys: stats.NewCpuStats(),
}
}

return nPids, nil
}