Re: [PATCH v3 6/7] drm/i915/perf: per-gen timebase for checking sample freq

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 05, 2017 at 06:17:36PM +0100, Lionel Landwerlin wrote:
> On 05/04/17 18:06, Ville Syrjälä wrote:
> > On Wed, Apr 05, 2017 at 05:23:19PM +0100, Robert Bragg wrote:
> >> An oa_exponent_to_ns() utility and per-gen timebase constants where
> >> recently removed when updating the tail pointer race condition WA, and
> >> this restores those so we can update the _PROP_OA_EXPONENT validation
> >> done in read_properties_unlocked() to not assume we have a 12.5KHz
> >> timebase as we did for Haswell.
> >>
> >> Signed-off-by: Robert Bragg <robert@sixbynine.org>
> >> Cc: Lionel Landwerlin <lionel.g.landwerlin@linux.intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/i915_drv.h  |  1 +
> >>   drivers/gpu/drm/i915/i915_perf.c | 21 +++++++++++++++------
> >>   2 files changed, 16 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> >> index 3a22b6fd0ee6..48b07d706f06 100644
> >> --- a/drivers/gpu/drm/i915/i915_drv.h
> >> +++ b/drivers/gpu/drm/i915/i915_drv.h
> >> @@ -2463,6 +2463,7 @@ struct drm_i915_private {
> >>   
> >>   			bool periodic;
> >>   			int period_exponent;
> >> +			int timestamp_frequency;
> >>   
> >>   			int metrics_set;
> >>   
> >> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> >> index 98eb6415b63a..87c0d1ce1b9f 100644
> >> --- a/drivers/gpu/drm/i915/i915_perf.c
> >> +++ b/drivers/gpu/drm/i915/i915_perf.c
> >> @@ -2549,6 +2549,12 @@ i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
> >>   	return ret;
> >>   }
> >>   
> >> +static u64 oa_exponent_to_ns(struct drm_i915_private *dev_priv, int exponent)
> >> +{
> >> +       return div_u64(1000000000ULL * (2ULL << exponent),
> >> +                      dev_priv->perf.oa.timestamp_frequency);
> >> +}
> >> +
> >>   /**
> >>    * read_properties_unlocked - validate + copy userspace stream open properties
> >>    * @dev_priv: i915 device instance
> >> @@ -2647,14 +2653,9 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
> >>   			/* Theoretically we can program the OA unit to sample
> >>   			 * every 160ns but don't allow that by default unless
> >>   			 * root.
> >> -			 *
> >> -			 * 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);
> >> +			oa_period = oa_exponent_to_ns(dev_priv, value);
> >>   
> >>   			/* This check is primarily to ensure that oa_period <=
> >>   			 * UINT32_MAX (before passing to do_div which only
> >> @@ -2910,6 +2911,8 @@ void i915_perf_init(struct drm_i915_private *dev_priv)
> >>   		dev_priv->perf.oa.ops.oa_hw_tail_read =
> >>   			gen7_oa_hw_tail_read;
> >>   
> >> +		dev_priv->perf.oa.timestamp_frequency = 12500000;
> >> +
> >>   		dev_priv->perf.oa.oa_formats = hsw_oa_formats;
> >>   
> >>   		dev_priv->perf.oa.n_builtin_sets =
> >> @@ -2923,6 +2926,8 @@ void i915_perf_init(struct drm_i915_private *dev_priv)
> >>   		 */
> >>   
> >>   		if (IS_GEN8(dev_priv)) {
> >> +			dev_priv->perf.oa.timestamp_frequency = 12500000;
> >> +
> >>   			dev_priv->perf.oa.ctx_oactxctrl_offset = 0x120;
> >>   			dev_priv->perf.oa.ctx_flexeu0_offset = 0x2ce;
> >>   			dev_priv->perf.oa.gen8_valid_ctx_bit = (1<<25);
> >> @@ -2939,6 +2944,8 @@ void i915_perf_init(struct drm_i915_private *dev_priv)
> >>   					i915_oa_select_metric_set_chv;
> >>   			}
> >>   		} else if (IS_GEN9(dev_priv)) {
> >> +			dev_priv->perf.oa.timestamp_frequency = 12000000;
> >> +
> >>   			dev_priv->perf.oa.ctx_oactxctrl_offset = 0x128;
> >>   			dev_priv->perf.oa.ctx_flexeu0_offset = 0x3de;
> >>   			dev_priv->perf.oa.gen8_valid_ctx_bit = (1<<16);
> >> @@ -2959,6 +2966,8 @@ void i915_perf_init(struct drm_i915_private *dev_priv)
> >>   				dev_priv->perf.oa.ops.select_metric_set =
> >>   					i915_oa_select_metric_set_sklgt4;
> >>   			} else if (IS_BROXTON(dev_priv)) {
> >> +				dev_priv->perf.oa.timestamp_frequency = 19200123;
> >> +
> > Why isn't this exactly 19.2MHz?
> 
> It's based off the timestamp base (from documentation) :
> 
> BDW: 80ns
> SKL: 83.333ns
> BXT: 52.083ns
> 
> 1000000000 / 19200123 is the closest we can get.

I'm pretty sure the clock is actually 19.2 and the 52.083 is just a
truncated value. Same for the 83.333 where the code does specify
120MHz exactly.

> 
> >
> >>   				dev_priv->perf.oa.n_builtin_sets =
> >>   					i915_oa_n_builtin_metric_sets_bxt;
> >>   				dev_priv->perf.oa.ops.select_metric_set =
> >> -- 
> >> 2.12.0
> >>
> >> _______________________________________________
> >> Intel-gfx mailing list
> >> Intel-gfx@lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 

-- 
Ville Syrjälä
Intel OTC
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