From 00319ba0434a99de12cb7241c136b5ef4aeaada7 Mon Sep 17 00:00:00 2001 From: Robert Bragg Date: Mon, 7 Nov 2016 19:49:55 +0000 Subject: [PATCH] drm/i915: add dev.i915.oa_max_sample_rate sysctl The maximum OA sampling frequency is now configurable via a dev.i915.oa_max_sample_rate sysctl parameter. Following the precedent set by perf's similar kernel.perf_event_max_sample_rate the default maximum rate is 100000Hz Signed-off-by: Robert Bragg Reviewed-by: Matthew Auld Reviewed-by: Sourab Gupta Signed-off-by: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/20161107194957.3385-10-robert@sixbynine.org --- drivers/gpu/drm/i915/i915_perf.c | 61 ++++++++++++++++++++++++++------ 1 file changed, 50 insertions(+), 11 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index e51c1d82255f..1a87fe967439 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -82,6 +82,21 @@ static u32 i915_perf_stream_paranoid = true; #define INVALID_CTX_ID 0xffffffff +/* For sysctl proc_dointvec_minmax of i915_oa_max_sample_rate + * + * 160ns is the smallest sampling period we can theoretically program the OA + * unit with on Haswell, corresponding to 6.25MHz. + */ +static int oa_sample_rate_hard_limit = 6250000; + +/* Theoretically we can program the OA unit to sample every 160ns but don't + * allow that by default unless root... + * + * The default threshold of 100000Hz is based on perf's similar + * kernel.perf_event_max_sample_rate sysctl parameter. + */ +static u32 i915_oa_max_sample_rate = 100000; + /* 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. @@ -1314,6 +1329,7 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv, } for (i = 0; i < n_props; i++) { + u64 oa_period, oa_freq_hz; u64 id, value; int ret; @@ -1359,21 +1375,35 @@ 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 + * On Haswell the period is derived from the exponent + * as: + * + * period = 80ns * 2^(exponent + 1) + */ + BUILD_BUG_ON(sizeof(oa_period) != 8); + oa_period = 80ull * (2ull << value); + + /* This check is primarily to ensure that oa_period <= + * UINT32_MAX (before passing to do_div which only + * accepts a u32 denominator), but we can also skip + * checking anything < 1Hz which implicitly can't be + * limited via an integer oa_max_sample_rate. */ - if (value < 6 && !capable(CAP_SYS_ADMIN)) { - DRM_ERROR("Minimum OA sampling exponent is 6 without root privileges\n"); + if (oa_period <= NSEC_PER_SEC) { + u64 tmp = NSEC_PER_SEC; + do_div(tmp, oa_period); + oa_freq_hz = tmp; + } else + oa_freq_hz = 0; + + if (oa_freq_hz > i915_oa_max_sample_rate && + !capable(CAP_SYS_ADMIN)) { + DRM_ERROR("OA exponent would exceed the max sampling frequency (sysctl dev.i915.oa_max_sample_rate) %uHz without root privileges\n", + i915_oa_max_sample_rate); return -EACCES; } @@ -1481,6 +1511,15 @@ static struct ctl_table oa_table[] = { .extra1 = &zero, .extra2 = &one, }, + { + .procname = "oa_max_sample_rate", + .data = &i915_oa_max_sample_rate, + .maxlen = sizeof(i915_oa_max_sample_rate), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &oa_sample_rate_hard_limit, + }, {} }; -- 2.20.1