On Wed, May 17, 2023 at 09:25:03AM -0700, Dixit, Ashutosh wrote:
On Wed, 17 May 2023 01:26:15 -0700, Tvrtko Ursulin wrote:
On 17/05/2023 07:55, Umesh Nerlige Ramappa wrote:
> 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.
First of all thanks for improving this, my v1 obviously wasn't good enough.
>>
>>> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>>>
>>> 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@xxxxxxxxx>
>>> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
>>> Cc: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx>
>>> ---
>>> 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.
Yeah that should be fine since -1 would make the below asserts fire
anyway. (If it would get called from a different path in the future.)
>>
>> 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.
Are you sure? I would have thought it would always be a compile time
constant now that the check is in config_mask. Aahhh.. with the multi-tile
changes maybe it can't unroll the loops and calculate the masks at compile
time. Maybe it is a bit too much and we should drop the
__builtin_constant_p branch? Probably..
Ah yes, with the code move to config_mask, they really all are compile time
constants (provided compiler can unroll the loops) so at least that is the
justfication for leaving the __builtin_constant_p in. So I'd probably just
leave it as is (though it is a bit too much).
But I guess it is safe to use GEM_WARN_ON_ONCE instead of WARN_ON_ONCE
since there are no external callers (nothing coming from event) now. That
way at least production builds don't have to have the check.
Hmm, there's a GEM_WARN_ON but no GEM_WARN_ON_ONCE. So leave that as is too
I guess.
So I'm ok with the code staying as is. Enough bike-shed on this already.
Leaving it as is. @Ashutosh, okay to use your R-b without any changes to
this patch?
Thanks,
Umesh
Thanks.
--
Ashutosh
Regards,
Tvrtko
>
> 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@xxxxxxxxx>
>>
>>> +
>>> + 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
>>>
