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 | 40 +++++++++++++++++++++++++++++----------- 1 file changed, 29 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index 7c27d93..ca4860b 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -41,6 +41,23 @@ static u32 i915_perf_stream_paranoid = true;
#define OA_EXPONENT_MAX 0x3f
+/* 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; + static struct i915_oa_format hsw_oa_formats[I915_OA_FORMAT_MAX] = { [I915_OA_FORMAT_A13] = { 0, 64 }, [I915_OA_FORMAT_A29] = { 1, 128 }, @@ -1098,20 +1115,12 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv, if (value > OA_EXPONENT_MAX) 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)) { + if (value < i915_oa_min_timer_exponent && + !capable(CAP_SYS_ADMIN)) { DRM_ERROR("Sampling period too high without root privileges\n"); return -EACCES; } @@ -1174,6 +1183,15 @@ 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, + }, {} };