[PATCH RFC 22/59] Use tsc for time rather than rumpkernel clock_gettime()

[Ronald Rojas <ronladred@gmail.com>]

From: George Dunlap <george.dunlap@citrix.com>

The rumpkernel clock_gettime() drifts drastically when the system is
overloaded.  Switch to using a TSC timesource instead:

* Use tsc_mode='native' in guest config
* Read the host tsc from /proc/cpuinfo when starting a run
* Pass it as an argument to the worker
* Implement now() with rdtsc

The results appear to continue to be accurate even with heavy
overcommitment.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
---
 benchmark.go |  8 ++++++++
 run.go       | 45 +++++++++++++++++++++++++++++++++++++++++++++
 xenworker.go |  1 +
 3 files changed, 54 insertions(+)

diff --git a/benchmark.go b/benchmark.go
index b0b55c7..7ea9aaa 100644
--- a/benchmark.go
+++ b/benchmark.go
@@ -48,6 +48,14 @@ type WorkerParams struct {
 	Args []string
 }
 
+func (l *WorkerParams) SetkHZ(kHZ uint64) {
+	if l.Args[0] == "kHZ" {
+		l.Args[1] = fmt.Sprintf("%d", kHZ)
+	} else {
+		l.Args = append([]string{"kHZ", fmt.Sprintf("%d", kHZ)}, l.Args...)
+	}
+}
+
 type WorkerConfig struct {
 	Pool string
 }
diff --git a/run.go b/run.go
index 2a93405..4222001 100644
--- a/run.go
+++ b/run.go
@@ -23,6 +23,9 @@ import (
 	"os"
 	"os/signal"
 	"time"
+	"regexp"
+	"strconv"
+	"bufio"
 )
 
 type WorkerState struct {
@@ -106,9 +109,45 @@ func NewWorkerList(WorkerSets []WorkerSet, workerType int) (wl WorkerList, err e
 	return
 }
 
+var CpukHZ uint64
+
+func getCpuHz() (err error) {
+	if CpukHZ == 0 {
+		var cpuinfo *os.File
+		cpuinfo, err = os.Open("/proc/cpuinfo")
+		if err != nil {
+			return
+		}
+		re := regexp.MustCompile("^cpu MHz\\s*: ([0-9.]+)$")
+		scanner := bufio.NewScanner(cpuinfo)
+		for scanner.Scan() {
+			s := scanner.Text()
+			m := re.FindStringSubmatch(s)
+			if m != nil {
+				var MHZ float64
+				MHZ, err = strconv.ParseFloat(m[1], 64)
+				if err != nil {
+					return
+				}
+				CpukHZ = uint64(MHZ*1000)
+				break
+			}
+		}
+		if CpukHZ == 0 {
+			err = fmt.Errorf("Couldn't find cpu MHz")
+			return
+		} else {
+			fmt.Println("CpukHZ: ", CpukHZ)
+			
+		}
+	}
+	return
+}
+
 func (run *BenchmarkRun) Run() (err error) {
 	for wsi := range run.WorkerSets {
 		run.WorkerSets[wsi].Config.PropagateFrom(run.WorkerConfig)
+		run.WorkerSets[wsi].Params.SetkHZ(CpukHZ)
 	}
 	
 	Workers, err := NewWorkerList(run.WorkerSets, WorkerXen)
@@ -164,6 +203,12 @@ func (run *BenchmarkRun) Run() (err error) {
 }
 
 func (plan *BenchmarkPlan) Run() (err error) {
+
+	err = getCpuHz()
+	if err != nil {
+		return
+	}
+	
 	for i := range plan.Runs {
 		r := &plan.Runs[i];
 		if ! r.Completed {
diff --git a/xenworker.go b/xenworker.go
index 4077e77..e98c970 100644
--- a/xenworker.go
+++ b/xenworker.go
@@ -95,6 +95,7 @@ func (w *XenWorker) Init(p WorkerParams, g WorkerConfig) (err error) {
 	fmt.Fprintf(cfg, "memory = 32\n")
 	fmt.Fprintf(cfg, "vcpus = 1\n")
 	fmt.Fprintf(cfg, "on_crash = 'destroy'\n")
+	fmt.Fprintf(cfg, "tsc_mode = 'native'\n")
 
 	if g.Pool != "" {
 		fmt.Fprintf(cfg, "pool = '%s'\n", g.Pool)
-- 
2.7.4


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