The minimal sampling period is now configurable via a
dev.i915.oa_min_timer_exponent sysctl parameter.
Following the precedent set by perf, the default is the minimum that
won't (on its own) exceed the default kernel.perf_event_max_sample_rate
default of 100000 samples/s.
Signed-off-by: Robert Bragg <robert@xxxxxxxxxxxxx>
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_perf.c | 42 ++++++++++++++++++++++++++++------------
1 file changed, 30 insertions(+), 12 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 4e42073..e3c6f51 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -82,6 +82,22 @@ static u32 i915_perf_stream_paranoid = true;
#define INVALID_CTX_ID 0xffffffff
+/* for sysctl proc_dointvec_minmax of i915_oa_min_timer_exponent */
+static int oa_exponent_max = OA_EXPONENT_MAX;
+
+/* Theoretically we can program the OA unit to sample every 160ns but don't
+ * allow that by default unless root...
+ *
+ * The period is derived from the exponent as:
+ *
+ * period = 80ns * 2^(exponent + 1)
+ *
+ * Referring to perf's kernel.perf_event_max_sample_rate for a precedent
+ * (100000 by default); with an OA exponent of 6 we get a period of 10.240
+ * microseconds - just under 100000Hz
+ */
+static u32 i915_oa_min_timer_exponent = 6;
+
/* XXX: beware if future OA HW adds new report formats that the current
* code assumes all reports have a power-of-two size and ~(size - 1) can
* be used as a mask to align the OA tail pointer.
@@ -1353,21 +1369,14 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
return -EINVAL;
}
- /* NB: The exponent represents a period as follows:
- *
- * 80ns * 2^(period_exponent + 1)
- *
- * Theoretically we can program the OA unit to sample
+ /* Theoretically we can program the OA unit to sample
* every 160ns but don't allow that by default unless
* root.
- *
- * Referring to perf's
- * kernel.perf_event_max_sample_rate for a precedent
- * (100000 by default); with an OA exponent of 6 we get
- * a period of 10.240 microseconds -just under 100000Hz
*/
- if (value < 6 && !capable(CAP_SYS_ADMIN)) {
- DRM_ERROR("Minimum OA sampling exponent is 6 without root privileges\n");
+ if (value < i915_oa_min_timer_exponent &&
+ !capable(CAP_SYS_ADMIN)) {
+ DRM_ERROR("Minimum OA sampling exponent (sysctl dev.i915.oa_min_timer_exponent) is %u without root privileges\n",
+ i915_oa_min_timer_exponent);
return -EACCES;
}
@@ -1475,6 +1484,15 @@ static struct ctl_table oa_table[] = {
.extra1 = &zero,
.extra2 = &one,
},
+ {
+ .procname = "oa_min_timer_exponent",
+ .data = &i915_oa_min_timer_exponent,
+ .maxlen = sizeof(i915_oa_min_timer_exponent),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &oa_exponent_max,
+ },
{}
};
--
2.10.1
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