Re: [Intel-gfx] [PATCH v5 1/7] drm/i915/pmu: Change bitmask of enabled events to u32

Umesh Nerlige Ramappa
2023-05-17T06:55:43Z

On Tue, May 16, 2023 at 05:25:50PM -0700, Dixit, Ashutosh wrote:
>On Tue, 16 May 2023 16:35:28 -0700, Umesh Nerlige Ramappa wrote:
>>
>
>Hi Umesh/Tvrtko,
>
>Mostly repeating comments/questions made on the previous patch below.
>
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> Having it as u64 was a confusing (but harmless) mistake.
>>
>> Also add some asserts to make sure the internal field does not overflow
>> in the future.
>>
>> v2: Fix WARN_ON firing for INTERRUPT event (Umesh)
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
>> Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
>> ---
>> drivers/gpu/drm/i915/i915_pmu.c | 26 ++++++++++++++++++--------
>> 1 file changed, 18 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
>> index 7ece883a7d95..96543dce2db1 100644
>> --- a/drivers/gpu/drm/i915/i915_pmu.c
>> +++ b/drivers/gpu/drm/i915/i915_pmu.c
>> @@ -50,7 +50,7 @@ static u8 engine_event_instance(struct perf_event *event)
>> return (event->attr.config >> I915_PMU_SAMPLE_BITS) & 0xff;
>> }
>>
>> -static bool is_engine_config(u64 config)
>> +static bool is_engine_config(const u64 config)
>> {
>> return config < __I915_PMU_OTHER(0);
>> }
>> @@ -88,9 +88,20 @@ static unsigned int config_bit(const u64 config)
>> return other_bit(config);
>> }
>>
>> -static u64 config_mask(u64 config)
>> +static u32 config_mask(const u64 config)
>> {
>> - return BIT_ULL(config_bit(config));
>> + unsigned int bit = config_bit(config);
>
>Give that config_bit() can return -1 (I understand it is avoided in moving
>the code to config_mask from config_bit), maybe the code below should also
>have that check?

config_mask is only called to check frequency related events in the
code, so I don't see it returing -1 here.

>
> int bit = config_bit(config);
>
> if (bit != -1)
> {
> ...
> }
>
>Though as mentioned below the 'if (__builtin_constant_p())' would have to
>go. Maybe the code could even have stayed in config_bit with the check.
>
>> +
>> + if (__builtin_constant_p(config))
>> + BUILD_BUG_ON(bit >
>> + BITS_PER_TYPE(typeof_member(struct i915_pmu,
>> + enable)) - 1);
>
>Given that config comes from the event (it is event->attr.config), can this
>ever be a builtin constant?

Not sure about earlier code where these checks were inside config_bit(),
but with changes I made, I don't see this being a builtin constant.
However, nothing prevents a caller from just passing a builtin_constant
to this in future.

Thanks,
Umesh

>
>> + else
>> + WARN_ON_ONCE(bit >
>> + BITS_PER_TYPE(typeof_member(struct i915_pmu,
>> + enable)) - 1);
>
>There is really an even stricter limit on what the bit can be, which is the
>total number of possible events but anyway this is good enough.
>
>After addressing the above, this patch is:
>
>Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
>
>> +
>> + return BIT(config_bit(config));
>> }
>>
>> static bool is_engine_event(struct perf_event *event)
>> @@ -633,11 +644,10 @@ static void i915_pmu_enable(struct perf_event *event)
>> {
>> struct drm_i915_private *i915 =
>> container_of(event->pmu, typeof(*i915), pmu.base);
>> + const unsigned int bit = event_bit(event);
>> struct i915_pmu *pmu = &i915->pmu;
>> unsigned long flags;
>> - unsigned int bit;
>>
>> - bit = event_bit(event);
>> if (bit == -1)
>> goto update;
>>
>> @@ -651,7 +661,7 @@ static void i915_pmu_enable(struct perf_event *event)
>> GEM_BUG_ON(bit >= ARRAY_SIZE(pmu->enable_count));
>> GEM_BUG_ON(pmu->enable_count[bit] == ~0);
>>
>> - pmu->enable |= BIT_ULL(bit);
>> + pmu->enable |= BIT(bit);
>> pmu->enable_count[bit]++;
>>
>> /*
>> @@ -698,7 +708,7 @@ static void i915_pmu_disable(struct perf_event *event)
>> {
>> struct drm_i915_private *i915 =
>> container_of(event->pmu, typeof(*i915), pmu.base);
>> - unsigned int bit = event_bit(event);
>> + const unsigned int bit = event_bit(event);
>> struct i915_pmu *pmu = &i915->pmu;
>> unsigned long flags;
>>
>> @@ -734,7 +744,7 @@ static void i915_pmu_disable(struct perf_event *event)
>> * bitmask when the last listener on an event goes away.
>> */
>> if (--pmu->enable_count[bit] == 0) {
>> - pmu->enable &= ~BIT_ULL(bit);
>> + pmu->enable &= ~BIT(bit);
>> pmu->timer_enabled &= pmu_needs_timer(pmu, true);
>> }
>>
>> --
>> 2.36.1
>>