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 --- 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 38b13fa..a7a248b 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -74,6 +74,23 @@ static u32 i915_perf_stream_paranoid = true; */ #define OA_EXPONENT_MAX 31
+/* for sysctl proc_dointvec_minmax of i915_oa_min_timer_exponent */ +static int zero; +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. @@ -1315,21 +1332,13 @@ 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("Sampling period too high without root privileges\n"); + if (value < i915_oa_min_timer_exponent && + !capable(CAP_SYS_ADMIN)) { + DRM_ERROR("OA timer exponent too low without root privileges\n"); return -EACCES; }
@@ -1433,6 +1442,15 @@ static struct ctl_table oa_table[] = { .mode = 0644, .proc_handler = proc_dointvec, }, + { + .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, + }, {} };