On Wed, Nov 2, 2016 at 6:29 AM, sourab gupta <sourab.gupta at intel.com> wrote:
> 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 at sixbynine.org> > > Reviewed-by: Matthew Auld <matthew.auld at 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? > actually it's bothered me a bit that I've been lazy with not having this adapt for gen9+ in later patches I think it would probably be better to make this a Hz based threshold for userspace, otherwise any userspace policy here needs to be adapted for each system with a different timestamp frequency which isn't great. I've updated the patch locally to make this an oa_max_sample_rate parameter in Hz, which I'll aim to test on haswell tomorrow and send out. Thanks, - Robert -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20161104/e60f1a57/attachment.html>
