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Index: share/man/man4/hwpmc.4
===================================================================
--- share/man/man4/hwpmc.4
+++ share/man/man4/hwpmc.4
@@ -416,6 +416,9 @@
.Nm Ns 's
logging function.
The default buffer size is 4KB.
+.It Va kern.hwpmc.mincount Pq integer, read-write
+The minimum sampling rate for sampling mode PMCs.
+The default count is 1000 events.
.It Va kern.hwpmc.mtxpoolsize Pq integer, read-only
The size of the spin mutex pool used by the PMC driver.
The default is 32.
Index: sys/dev/hwpmc/hwpmc_mod.c
===================================================================
--- sys/dev/hwpmc/hwpmc_mod.c
+++ sys/dev/hwpmc/hwpmc_mod.c
@@ -366,6 +366,14 @@
"maximum number of available thread entries before freeing some");
+/*
+ * kern.hwpmc.mincount -- minimum sample count
+ */
+static u_int pmc_mincount = 1000;
+SYSCTL_INT(_kern_hwpmc, OID_AUTO, mincount, CTLFLAG_RWTUN,
+ &pmc_mincount, 0,
+ "minimum count for sampling counters");
+
/*
* security.bsd.unprivileged_syspmcs -- allow non-root processes to
* allocate system-wide PMCs.
@@ -3951,13 +3959,16 @@
/* XXX set lower bound on sampling for process counters */
if (PMC_IS_SAMPLING_MODE(mode)) {
/*
- * Don't permit requested sample rate to be less than 1000
+ * Don't permit requested sample rate to be
+ * less than pmc_mincount.
*/
- if (pa.pm_count < 1000)
- log(LOG_WARNING,
- "pmcallocate: passed sample rate %ju - setting to 1000\n",
- (uintmax_t)pa.pm_count);
- pmc->pm_sc.pm_reloadcount = MAX(1000, pa.pm_count);
+ if (pa.pm_count < MAX(1, pmc_mincount))
+ log(LOG_WARNING, "pmcallocate: passed sample "
+ "rate %ju - setting to %u\n",
+ (uintmax_t)pa.pm_count,
+ MAX(1, pmc_mincount));
+ pmc->pm_sc.pm_reloadcount = MAX(MAX(1, pmc_mincount),
+ pa.pm_count);
} else
pmc->pm_sc.pm_initial = pa.pm_count;
@@ -4475,13 +4486,16 @@
if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm))) {
/*
- * Don't permit requested sample rate to be less than 1000
+ * Don't permit requested sample rate to be
+ * less than pmc_mincount.
*/
- if (sc.pm_count < 1000)
- log(LOG_WARNING,
- "pmcsetcount: passed sample rate %ju - setting to 1000\n",
- (uintmax_t)sc.pm_count);
- pm->pm_sc.pm_reloadcount = MAX(1000, sc.pm_count);
+ if (sc.pm_count < MAX(1, pmc_mincount))
+ log(LOG_WARNING, "pmcsetcount: passed sample "
+ "rate %ju - setting to %u\n",
+ (uintmax_t)sc.pm_count,
+ MAX(1, pmc_mincount));
+ pm->pm_sc.pm_reloadcount = MAX(MAX(1, pmc_mincount),
+ sc.pm_count);
} else
pm->pm_sc.pm_initial = sc.pm_count;
}

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