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authorLen Brown <len.brown@intel.com>2012-03-29 21:44:40 -0400
committerLen Brown <len.brown@intel.com>2012-03-29 22:04:58 -0400
commit88c3281f7ba449992f7a33bd2452a8c6fa5503cb (patch)
tree09199b6751bbff93feb014c23fa48c736c5c6a59 /tools
parente23da0370f80834e971142e50253f5b79be83631 (diff)
tools turbostat: reduce measurement overhead due to IPIs
turbostat uses /dev/cpu/*/msr interface to read MSRs. For modern systems, it reads 10 MSR/CPU. This can be observed as 10 "Function Call Interrupts" per CPU per sample added to /proc/interrupts. This overhead is measurable on large idle systems, and as Yoquan Song pointed out, it can even trick cpuidle into thinking the system is busy. Here turbostat re-schedules itself in-turn to each CPU so that its MSR reads will always be local. This replaces the 10 "Function Call Interrupts" with a single "Rescheduling interrupt" per sample per CPU. On an idle 32-CPU system, this shifts some residency from the shallow c1 state to the deeper c7 state: # ./turbostat.old -s %c0 GHz TSC %c1 %c3 %c6 %c7 %pc2 %pc3 %pc6 %pc7 0.27 1.29 2.29 0.95 0.02 0.00 98.77 20.23 0.00 77.41 0.00 0.25 1.24 2.29 0.98 0.02 0.00 98.75 20.34 0.03 77.74 0.00 0.27 1.22 2.29 0.54 0.00 0.00 99.18 20.64 0.00 77.70 0.00 0.26 1.22 2.29 1.22 0.00 0.00 98.52 20.22 0.00 77.74 0.00 0.26 1.38 2.29 0.78 0.02 0.00 98.95 20.51 0.05 77.56 0.00 ^C i# ./turbostat.new -s %c0 GHz TSC %c1 %c3 %c6 %c7 %pc2 %pc3 %pc6 %pc7 0.27 1.20 2.29 0.24 0.01 0.00 99.49 20.58 0.00 78.20 0.00 0.27 1.22 2.29 0.25 0.00 0.00 99.48 20.79 0.00 77.85 0.00 0.27 1.20 2.29 0.25 0.02 0.00 99.46 20.71 0.03 77.89 0.00 0.28 1.26 2.29 0.25 0.01 0.00 99.46 20.89 0.02 77.67 0.00 0.27 1.20 2.29 0.24 0.01 0.00 99.48 20.65 0.00 78.04 0.00 cc: Youquan Song <youquan.song@intel.com> Signed-off-by: Len Brown <len.brown@intel.com>
Diffstat (limited to 'tools')
-rw-r--r--tools/power/x86/turbostat/turbostat.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index 6436d54378c7..fa60872b9474 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -19,6 +19,7 @@
* 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
*/
+#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
@@ -32,6 +33,7 @@
#include <dirent.h>
#include <string.h>
#include <ctype.h>
+#include <sched.h>
#define MSR_TSC 0x10
#define MSR_NEHALEM_PLATFORM_INFO 0xCE
@@ -72,6 +74,8 @@ char *progname;
int need_reinitialize;
int num_cpus;
+cpu_set_t *cpu_mask;
+size_t cpu_mask_size;
struct counters {
unsigned long long tsc; /* per thread */
@@ -100,6 +104,40 @@ struct timeval tv_even;
struct timeval tv_odd;
struct timeval tv_delta;
+/*
+ * cpu_mask_init(ncpus)
+ *
+ * allocate and clear cpu_mask
+ * set cpu_mask_size
+ */
+void cpu_mask_init(int ncpus)
+{
+ cpu_mask = CPU_ALLOC(ncpus);
+ if (cpu_mask == NULL) {
+ perror("CPU_ALLOC");
+ exit(3);
+ }
+ cpu_mask_size = CPU_ALLOC_SIZE(ncpus);
+ CPU_ZERO_S(cpu_mask_size, cpu_mask);
+}
+
+void cpu_mask_uninit()
+{
+ CPU_FREE(cpu_mask);
+ cpu_mask = NULL;
+ cpu_mask_size = 0;
+}
+
+int cpu_migrate(int cpu)
+{
+ CPU_ZERO_S(cpu_mask_size, cpu_mask);
+ CPU_SET_S(cpu, cpu_mask_size, cpu_mask);
+ if (sched_setaffinity(0, cpu_mask_size, cpu_mask) == -1)
+ return -1;
+ else
+ return 0;
+}
+
unsigned long long get_msr(int cpu, off_t offset)
{
ssize_t retval;
@@ -471,6 +509,11 @@ void compute_average(struct counters *delta, struct counters *avg)
void get_counters(struct counters *cnt)
{
for ( ; cnt; cnt = cnt->next) {
+ if (cpu_migrate(cnt->cpu)) {
+ need_reinitialize = 1;
+ return;
+ }
+
cnt->tsc = get_msr(cnt->cpu, MSR_TSC);
if (do_nhm_cstates)
cnt->c3 = get_msr(cnt->cpu, MSR_CORE_C3_RESIDENCY);
@@ -752,6 +795,8 @@ void re_initialize(void)
free_all_counters();
num_cpus = for_all_cpus(alloc_new_counters);
need_reinitialize = 0;
+ cpu_mask_uninit();
+ cpu_mask_init(num_cpus);
printf("num_cpus is now %d\n", num_cpus);
}
@@ -984,6 +1029,7 @@ void turbostat_init()
check_super_user();
num_cpus = for_all_cpus(alloc_new_counters);
+ cpu_mask_init(num_cpus);
if (verbose)
print_nehalem_info();

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