tools/power turbostat: make fewer systems calls

skip the open(2)/close(2) on each msr read
by keeping the /dev/cpu/*/msr files open.

The remaining read(2) is generally far fewer cycles
than the removed open(2) system call.

Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 41 insertions, 10 deletions

diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index ad5bd5600467..2e47c2bc3e27 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -45,6 +45,7 @@
 
 char *proc_stat = "/proc/stat";
 FILE *outf;
+int *fd_percpu;
 struct timespec interval_ts = {5, 0};
 unsigned int debug;
 unsigned int rapl_joules;
@@ -270,23 +271,34 @@ int cpu_migrate(int cpu)
         else
                 return 0;
 }
-
-int get_msr(int cpu, off_t offset, unsigned long long *msr)
+int get_msr_fd(int cpu)
 {
-        ssize_t retval;
         char pathname[32];
         int fd;
 
+        fd = fd_percpu[cpu];
+
+        if (fd)
+                return fd;
+
         sprintf(pathname, "/dev/cpu/%d/msr", cpu);
         fd = open(pathname, O_RDONLY);
         if (fd < 0)
                 err(-1, "%s open failed, try chown or chmod +r /dev/cpu/*/msr, or run as root", pathname);
 
-        retval = pread(fd, msr, sizeof *msr, offset);
-        close(fd);
+        fd_percpu[cpu] = fd;
+
+        return fd;
+}
+
+int get_msr(int cpu, off_t offset, unsigned long long *msr)
+{
+        ssize_t retval;
+
+        retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
 
         if (retval != sizeof *msr)
-                err(-1, "%s offset 0x%llx read failed", pathname, (unsigned long long)offset);
+                err(-1, "msr %d offset 0x%llx read failed", cpu, (unsigned long long)offset);
 
         return 0;
 }
@@ -1453,19 +1465,30 @@ dump_config_tdp(void)
                 fprintf(outf, "TDP_LEVEL=%d ", (unsigned int)(msr) & 0x3);
         fprintf(outf, " lock=%d", (unsigned int)(msr >> 31) & 1);
         fprintf(outf, ")\n");
-        
+
         get_msr(base_cpu, MSR_TURBO_ACTIVATION_RATIO, &msr);
         fprintf(outf, "cpu%d: MSR_TURBO_ACTIVATION_RATIO: 0x%08llx (", base_cpu, msr);
         fprintf(outf, "MAX_NON_TURBO_RATIO=%d", (unsigned int)(msr) & 0x7F);
         fprintf(outf, " lock=%d", (unsigned int)(msr >> 31) & 1);
         fprintf(outf, ")\n");
 }
+void free_fd_percpu(void)
+{
+        int i;
+
+        for (i = 0; i < topo.max_cpu_num; ++i) {
+                if (fd_percpu[i] != 0)
+                        close(fd_percpu[i]);
+        }
+
+        free(fd_percpu);
+}
 
 void free_all_buffers(void)
 {
         CPU_FREE(cpu_present_set);
         cpu_present_set = NULL;
-        cpu_present_set = 0;
+        cpu_present_setsize = 0;
 
         CPU_FREE(cpu_affinity_set);
         cpu_affinity_set = NULL;
@@ -1490,6 +1513,8 @@ void free_all_buffers(void)
         free(output_buffer);
         output_buffer = NULL;
         outp = NULL;
+
+        free_fd_percpu();
 }
 
 /*
@@ -2449,7 +2474,7 @@ int print_thermal(struct thread_data *t, struct core_data *c, struct pkg_data *p
 
         return 0;
 }
-        
+
 void print_power_limit_msr(int cpu, unsigned long long msr, char *label)
 {
         fprintf(outf, "cpu%d: %s: %sabled (%f Watts, %f sec, clamp %sabled)\n",
@@ -3202,10 +3227,16 @@ void allocate_output_buffer()
         if (outp == NULL)
                 err(-1, "calloc output buffer");
 }
-
+void allocate_fd_percpu(void)
+{
+        fd_percpu = calloc(topo.max_cpu_num, sizeof(int));
+        if (fd_percpu == NULL)
+                err(-1, "calloc fd_percpu");
+}
 void setup_all_buffers(void)
 {
         topology_probe();
+        allocate_fd_percpu();
         allocate_counters(&thread_even, &core_even, &package_even);
         allocate_counters(&thread_odd, &core_odd, &package_odd);
         allocate_output_buffer();