Re: [PATCH 14/17] drm/i915: Add stats for GuC log buffer flush interrupts

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 18/07/16 11:59, Goel, Akash wrote:
> On 7/18/2016 3:46 PM, Tvrtko Ursulin wrote:
>>
>> On 15/07/16 16:58, Goel, Akash wrote:
>>> On 7/15/2016 5:21 PM, Tvrtko Ursulin wrote:
>>>> On 10/07/16 14:41, akash.goel@intel.com wrote:
>>>>> From: Akash Goel <akash.goel@intel.com>
>>>>>
>>>>> GuC firmware sends an interrupt to flush the log buffer when it
>>>>> becomes half full. GuC firmware also tracks how many times the
>>>>> buffer overflowed.
>>>>> It would be useful to maintain a statistics of how many flush
>>>>> interrupts were received and for which type of log buffer,
>>>>> along with the overflow count of each buffer type.
>>>>> Augmented i915_log_info debugfs to report back these statistics.
>>>>>
>>>>> Signed-off-by: Akash Goel <akash.goel@intel.com>
>>>>> ---
>>>>>   drivers/gpu/drm/i915/i915_debugfs.c        | 26
>>>>> ++++++++++++++++++++++++++
>>>>>   drivers/gpu/drm/i915/i915_guc_submission.c |  8 ++++++++
>>>>>   drivers/gpu/drm/i915/i915_irq.c            |  1 +
>>>>>   drivers/gpu/drm/i915/intel_guc.h           |  6 ++++++
>>>>>   4 files changed, 41 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
>>>>> b/drivers/gpu/drm/i915/i915_debugfs.c
>>>>> index 3c9c7f7..888a18a 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_debugfs.c
>>>>> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
>>>>> @@ -2538,6 +2538,30 @@ static int i915_guc_load_status_info(struct
>>>>> seq_file *m, void *data)
>>>>>       return 0;
>>>>>   }
>>>>>
>>>>> +static void i915_guc_log_info(struct seq_file *m,
>>>>> +                 struct drm_i915_private *dev_priv)
>>>>> +{
>>>>> +    struct intel_guc *guc = &dev_priv->guc;
>>>>> +
>>>>> +    seq_printf(m, "\nGuC logging stats:\n");
>>>>> +
>>>>> +    seq_printf(m, "\tISR:   flush count %10u, overflow count %8u\n",
>>>>> +        guc->log.flush_count[GUC_ISR_LOG_BUFFER],
>>>>> +        guc->log.total_overflow_count[GUC_ISR_LOG_BUFFER]);
>>>>> +
>>>>> +    seq_printf(m, "\tDPC:   flush count %10u, overflow count %8u\n",
>>>>> +        guc->log.flush_count[GUC_DPC_LOG_BUFFER],
>>>>> +        guc->log.total_overflow_count[GUC_DPC_LOG_BUFFER]);
>>>>> +
>>>>> +    seq_printf(m, "\tCRASH: flush count %10u, overflow count %8u\n",
>>>>> +        guc->log.flush_count[GUC_CRASH_DUMP_LOG_BUFFER],
>>>>> +        guc->log.total_overflow_count[GUC_CRASH_DUMP_LOG_BUFFER]);
>>>>> +
>>>>> +    seq_printf(m, "\tTotal flush interrupt count: %u\n",
>>>>> +            guc->log.flush_interrupt_count);
>>>>> +
>>>>> +}
>>>>> +
>>>>>   static void i915_guc_client_info(struct seq_file *m,
>>>>>                    struct drm_i915_private *dev_priv,
>>>>>                    struct i915_guc_client *client)
>>>>> @@ -2611,6 +2635,8 @@ static int i915_guc_info(struct seq_file *m,
>>>>> void *data)
>>>>>       seq_printf(m, "\nGuC execbuf client @ %p:\n",
>>>>> guc.execbuf_client);
>>>>>       i915_guc_client_info(m, dev_priv, &client);
>>>>>
>>>>> +    i915_guc_log_info(m, dev_priv);
>>>>> +
>>>>>       /* Add more as required ... */
>>>>>
>>>>>       return 0;
>>>>> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> b/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> index c1e637f..9c94a43 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
>>>>> @@ -914,6 +914,14 @@ static void guc_read_update_log_buffer(struct
>>>>> drm_device *dev)
>>>>>           log_buffer_state_local = *log_buffer_state;
>>>>>           buffer_size = log_buffer_state_local.size;
>>>>>
>>>>> +        guc->log.flush_count[i] +=
>>>>> log_buffer_state_local.flush_to_file;
>>>>> +        if (log_buffer_state_local.buffer_full_cnt !=
>>>>> +                    guc->log.prev_overflow_count[i]) {
>>>>> +            guc->log.prev_overflow_count[i] =
>>>>> +                    log_buffer_state_local.buffer_full_cnt;
>>>>> +            guc->log.total_overflow_count[i]++;
>>>>
>>>> Is log_buffer_state_local.buffer_full_cnt guaranteed to be one here? Or
>>>> you would need to increase total_overflow_count by its value?
>>>>
>>>
>>> buffer_full_cnt will not remain as one. Its a 4 bit counter, will be
>>> incremented monotonically by GuC firmware on every new detection of
>>> overflow, so will increase from 0 to 15 & then wrap around.
>>> Hence have to use '!=' in the condition instead of '>'.
>>
>> But can it happen that it jumps by more than one between being sampled
>> here? In which case you would need to replace:
>>
>> guc->log.total_overflow_count[i]++;
>>
>> by something like:
>>
>>
>> guc->log.total_overflow_count[i] +=
>> log_buffer_state_local.buffer_full_cnt - guc->log.prev_overflow_count[i];
>>
>> (Doesn't handle the wrap though, just to illustrate my point.)
>>
> Actually logic in GuC firmware is such that overflow counter cannot
> increment by more than 1 without Driver coming into picture in between,
> by the virtue of flush interrupt.

Hm, and what happens to the data and overflow counter if the driver is 
not responsive enough?

> But nevertheless the logic on Driver side should be like the way you
> suggested.
>
> Does this revised logic looks fine ?
>
> if (log_buffer_state_local.buffer_full_cnt !=
>          guc->log.prev_overflow_count[i]) {
>      new_overflow = 1;
>      guc->log.total_overflow_count[i] +=
> (log_buffer_state_local.buffer_full_cnt - guc->log.prev_overflow_count[i]);
>
>      if (log_buffer_state_local.buffer_full_cnt <
> guc->log.prev_overflow_count[i])
>          guc->log.total_overflow_count[i] += 15;
>
>      log_buffer_state_local.buffer_full_cnt =
> guc->log.prev_overflow_count[i];
> }

Not sure, maybe += 16 ? If counter goes from 15 to zero, then -15, +15 = 
no change which is wrong?

But in general if the condition should not happen I would also put a 
WARN_ON_ONCE or a rate limited DRM_ERROR in that case.

Regards,

Tvrtko


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