Move sysfs-reading code to LinuxProcessList.c and add average frequency.

This way the frequency is read from sysfs only once per update cycle
instead of every time the UI is redrawn.

This also changes the code to read from /proc/cpuinfo instead. This is because
reading from scaling_cur_freq stalls for 10ms if the previous read for the file
was more than one second ago. [1] Since htop's update cycle is
longer than that, it would cause the read of each CPU's scaling_cur_freq file
to block the UI for 20ms. This easily led to a noticeable half-second lag on
a 20+ CPU machine.

/proc/cpuinfo also has a 10ms delay, but this applies for the whole file
so the delay does not scale with the number of CPUs. [2]

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4815d3c56d1e10449a44089a47544d9ba84fad0d
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d5905dc14a87805a59f3c5bf70173aac2bb18f8

4 files changed, 84 insertions, 21 deletions

diff --git a/CPUMeter.c b/CPUMeter.c
index edcd61d2..6785410e 100644
--- a/CPUMeter.c
+++ b/CPUMeter.c
@@ -64,20 +64,16 @@ static void CPUMeter_updateValues(Meter* this, char* buffer, int size) {
    }
    memset(this->values, 0, sizeof(double) * CPU_METER_ITEMCOUNT);
    double percent = Platform_setCPUValues(this, cpu);
-   if (cpu != 0 && this->pl->settings->showCPUFrequency) {
-      /* Initial frequency is in KHz. Divide it by 1000 till it's less than 1000, and emit unit accordingly */
+   if (this->pl->settings->showCPUFrequency) {
+      /* Initial frequency is in MHz. Emit it as GHz if it's larger than 1000MHz */
       double cpuFrequency = this->values[CPU_METER_FREQUENCY];
-      char unit = 'K';
+      char unit = 'M';
       char cpuFrequencyBuffer[16];
       if (cpuFrequency < 0) {
          xSnprintf(cpuFrequencyBuffer, sizeof(cpuFrequencyBuffer), "N/A");
       } else {
          if (cpuFrequency > 1000) {
             cpuFrequency /= 1000;
-            unit = 'M';
-         }
-         if (cpuFrequency > 1000) {
-            cpuFrequency /= 1000;
             unit = 'G';
          }
          xSnprintf(cpuFrequencyBuffer, sizeof(cpuFrequencyBuffer), "%.3f%cHz", cpuFrequency, unit);
diff --git a/linux/LinuxProcessList.c b/linux/LinuxProcessList.c
index 5f38540c..39f8405f 100644
--- a/linux/LinuxProcessList.c
+++ b/linux/LinuxProcessList.c
@@ -75,6 +75,8 @@ typedef struct CPUData_ {
    unsigned long long int softIrqPeriod;
    unsigned long long int stealPeriod;
    unsigned long long int guestPeriod;
+
+   double frequency;
 } CPUData;
 
 typedef struct TtyDriver_ {
@@ -100,6 +102,10 @@ typedef struct LinuxProcessList_ {
 #define PROCDIR "/proc"
 #endif
 
+#ifndef PROCCPUINFOFILE
+#define PROCCPUINFOFILE PROCDIR "/cpuinfo"
+#endif
+
 #ifndef PROCSTATFILE
 #define PROCSTATFILE PROCDIR "/stat"
 #endif
@@ -1028,18 +1034,86 @@ static inline double LinuxProcessList_scanCPUTime(LinuxProcessList* this) {
       cpuData->stealTime = steal;
       cpuData->guestTime = virtalltime;
       cpuData->totalTime = totaltime;
+
    }
    double period = (double)this->cpus[0].totalPeriod / cpus;
    fclose(file);
    return period;
 }
 
+static inline double LinuxProcessList_scanCPUFrequency(LinuxProcessList* this) {
+   ProcessList* pl = (ProcessList*) this;
+   Settings* settings = pl->settings;
+
+   int cpus = this->super.cpuCount;
+   assert(cpus > 0);
+
+   for (int i = 0; i <= cpus; i++) {
+      CPUData* cpuData = &(this->cpus[i]);
+      cpuData->frequency = -1;
+   }
+
+   int numCPUsWithFrequency = 0;
+   double totalFrequency = 0;
+
+   if (settings->showCPUFrequency) {
+      FILE* file = fopen(PROCCPUINFOFILE, "r");
+      if (file == NULL) {
+         CRT_fatalError("Cannot open " PROCCPUINFOFILE);
+      }
+
+      int cpuid = -1;
+      double frequency;
+      while (!feof(file)) {
+         char buffer[PROC_LINE_LENGTH];
+         char *ok = fgets(buffer, PROC_LINE_LENGTH, file);
+         if (!ok) break;
+
+         if (
+            (sscanf(buffer, "processor : %d", &cpuid) == 1) ||
+            (sscanf(buffer, "processor: %d", &cpuid) == 1)
+         ) {
+            if (cpuid < 0 || cpuid > (cpus - 1)) {
+               char buffer[64];
+               xSnprintf(buffer, sizeof(buffer), PROCCPUINFOFILE " contains out-of-range CPU number %d", cpuid);
+               CRT_fatalError(buffer);
+            }
+         } else if (
+            (sscanf(buffer, "cpu MHz : %lf", &frequency) == 1) ||
+            (sscanf(buffer, "cpu MHz: %lf", &frequency) == 1)
+         ) {
+            if (cpuid < 0) {
+               CRT_fatalError(PROCCPUINFOFILE " is malformed: cpu MHz line without corresponding processor line");
+            }
+
+            int cpu = cpuid + 1;
+            CPUData* cpuData = &(this->cpus[cpu]);
+            cpuData->frequency = frequency;
+            numCPUsWithFrequency++;
+            totalFrequency += frequency;
+         } else if (buffer[0] == '\n') {
+            cpuid = -1;
+         }
+      }
+      fclose(file);
+
+      if (numCPUsWithFrequency > 0) {
+         this->cpus[0].frequency = totalFrequency / numCPUsWithFrequency;
+      }
+   }
+
+   double period = (double)this->cpus[0].totalPeriod / cpus;
+   return period;
+}
+
 void ProcessList_goThroughEntries(ProcessList* super) {
    LinuxProcessList* this = (LinuxProcessList*) super;
 
    LinuxProcessList_scanMemoryInfo(super);
    double period = LinuxProcessList_scanCPUTime(this);
 
+   LinuxProcessList_scanCPUFrequency(this);
+
    struct timeval tv;
    gettimeofday(&tv, NULL);
    LinuxProcessList_recurseProcTree(this, PROCDIR, NULL, period, tv);
diff --git a/linux/LinuxProcessList.h b/linux/LinuxProcessList.h
index f30b487d..ae36b354 100644
--- a/linux/LinuxProcessList.h
+++ b/linux/LinuxProcessList.h
@@ -48,6 +48,8 @@ typedef struct CPUData_ {
    unsigned long long int softIrqPeriod;
    unsigned long long int stealPeriod;
    unsigned long long int guestPeriod;
+
+   double frequency;
 } CPUData;
 
 typedef struct TtyDriver_ {
@@ -73,6 +75,10 @@ typedef struct LinuxProcessList_ {
 #define PROCDIR "/proc"
 #endif
 
+#ifndef PROCCPUINFOFILE
+#define PROCCPUINFOFILE PROCDIR "/cpuinfo"
+#endif
+
 #ifndef PROCSTATFILE
 #define PROCSTATFILE PROCDIR "/stat"
 #endif
diff --git a/linux/Platform.c b/linux/Platform.c
index fc81d3bf..806d4c00 100644
--- a/linux/Platform.c
+++ b/linux/Platform.c
@@ -193,20 +193,7 @@ double Platform_setCPUValues(Meter* this, int cpu) {
    percent = CLAMP(percent, 0.0, 100.0);
    if (isnan(percent)) percent = 0.0;
 
-   v[CPU_METER_FREQUENCY] = -1;
-   if (this->pl->settings->showCPUFrequency) {
-      char filename[64];
-      xSnprintf(filename, sizeof(filename), "/sys/devices/system/cpu/cpu%d/cpufreq/scaling_cur_freq", cpu - 1);
-      FILE* fd = fopen(filename, "r");
-      if (fd) {
-         unsigned int cpuFrequency;
-         int n = fscanf(fd, "%u", &cpuFrequency);
-         fclose(fd);
-         if (n > 0) {
-            v[CPU_METER_FREQUENCY] = cpuFrequency;
-         }
-      }
-   }
+   v[CPU_METER_FREQUENCY] = cpuData->frequency;
 
    return percent;
 }