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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 <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Sourab Gupta <sourab.gupta@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161107194957.3385-10-robert@sixbynine.org
This commit is contained in:
Robert Bragg 2016-11-07 19:49:55 +00:00 committed by Daniel Vetter
parent ccdf6341ed
commit 00319ba043
1 changed files with 50 additions and 11 deletions
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61
drivers/gpu/drm/i915/i915_perf.c
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@ -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)
*/
if (value < 6 && !capable(CAP_SYS_ADMIN)) {
DRM_ERROR("Minimum OA sampling exponent is 6 without root privileges\n");
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 (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,
},
{}
};