On Thu, 2016-10-27 at 19:14 -0700, Robert Bragg wrote:
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@sixbynine.org Reviewed-by: Matthew Auld matthew.auld@intel.com
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;
For HSW, the timestamp period is 80ns, so the exponent of 6 translates to sampling rate of ~100000Hz. But the timestamp period may change for other platforms, leading to different values of oa_min_timer_exponent corresponding to sampling rate of ~100000Hz. Do we plan to have this value platform specific subsequently, or the guidance value of ~100000Hz min sampling rate needn't be strictly followed?
/* 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,},};