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

[Lionel Landwerlin <lionel.g.landwerlin@linux.intel.com>]

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.

>
>>   				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
>>
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>> Intel-gfx@lists.freedesktop.org
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