cmd/syncthing: Use a 10 second EWMA for CPU usage, refactor a little

We have it lying around so might as well use it instead of inventing our
own thing.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4111

cmd/syncthing/cpuusage_solaris.go

@@ -0,0 +1,78 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//+build solaris
+
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"os"
+	"time"
+)
+
+type id_t int32
+type ulong_t uint32
+
+type timestruc_t struct {
+	Tv_sec  int64
+	Tv_nsec int64
+}
+
+func (tv timestruc_t) Nano() int64 {
+	return tv.Tv_sec*1e9 + tv.Tv_nsec
+}
+
+type prusage_t struct {
+	Pr_lwpid    id_t        /* lwp id.  0: process or defunct */
+	Pr_count    int32       /* number of contributing lwps */
+	Pr_tstamp   timestruc_t /* real time stamp, time of read() */
+	Pr_create   timestruc_t /* process/lwp creation time stamp */
+	Pr_term     timestruc_t /* process/lwp termination time stamp */
+	Pr_rtime    timestruc_t /* total lwp real (elapsed) time */
+	Pr_utime    timestruc_t /* user level CPU time */
+	Pr_stime    timestruc_t /* system call CPU time */
+	Pr_ttime    timestruc_t /* other system trap CPU time */
+	Pr_tftime   timestruc_t /* text page fault sleep time */
+	Pr_dftime   timestruc_t /* data page fault sleep time */
+	Pr_kftime   timestruc_t /* kernel page fault sleep time */
+	Pr_ltime    timestruc_t /* user lock wait sleep time */
+	Pr_slptime  timestruc_t /* all other sleep time */
+	Pr_wtime    timestruc_t /* wait-cpu (latency) time */
+	Pr_stoptime timestruc_t /* stopped time */
+	Pr_minf     ulong_t     /* minor page faults */
+	Pr_majf     ulong_t     /* major page faults */
+	Pr_nswap    ulong_t     /* swaps */
+	Pr_inblk    ulong_t     /* input blocks */
+	Pr_oublk    ulong_t     /* output blocks */
+	Pr_msnd     ulong_t     /* messages sent */
+	Pr_mrcv     ulong_t     /* messages received */
+	Pr_sigs     ulong_t     /* signals received */
+	Pr_vctx     ulong_t     /* voluntary context switches */
+	Pr_ictx     ulong_t     /* involuntary context switches */
+	Pr_sysc     ulong_t     /* system calls */
+	Pr_ioch     ulong_t     /* chars read and written */
+
+}
+
+var procFile = fmt.Sprintf("/proc/%d/usage", os.Getpid())
+
+func cpuUsage() time.Duration {
+	fd, err := os.Open(procFile)
+	if err != nil {
+		return 0
+	}
+
+	var rusage prusage_t
+	err = binary.Read(fd, binary.LittleEndian, rusage)
+	fd.Close()
+	if err != nil {
+		return 0
+	}
+
+	return time.Duration(rusage.Pr_utime.Nano() + rusage.Pr_stime.Nano())
+}