[Intel-gfx] [PATCH 7/7] drm/i915/perf: add flushing ioctl

[Joonas Lahtinen]

Quoting Lionel Landwerlin (2019-02-04 17:30:12)
> On 22/01/2019 16:25, Joonas Lahtinen wrote:
> > Quoting Lionel Landwerlin (2019-01-16 17:36:22)
> >> With the currently available parameters for the i915-perf stream,
> >> there are still situations that are not well covered :
> >>
> >> If an application opens the stream with polling disable or at very low
> >> frequency and OA interrupt enabled, no data will be available even
> >> though somewhere between nothing and half of the OA buffer worth of
> >> data might have landed in memory.
> >>
> >> To solve this issue we have a new flush ioctl on the perf stream that
> >> forces the i915-perf driver to look at the state of the buffer when
> >> called and makes any data available through both poll() & read() type
> >> syscalls.
> >>
> >> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> > Link to userspace changes?
> >
> > Regards, Joonas
> 
> 
> Hey Joonas,
> 
> 
> I'm about to make the changes in gputop for the high frequency sampling 
> use case.
> 
> 
> One thing I would like to know is whether these new features should be 
> reported through a flag.
> 
> So far we haven't added any new option to the i915/perf driver since the 
> initial upstreaming series.
> 
> 
> The way I'm currently detecting newly added parameters is by using 
> trying to open the stream with a value that I know will report ENOENT 
> rather than EINVAL when the feature is not available :
> 
> https://github.com/djdeath/intel-gpu-tools/blob/wip/djdeath/oa-interrupts/tests/perf.c#L4345
> 
> Is there a better way to do this?

I think I already responded in IRC, but here goes for e-mail archives.

A GETPARAM with rolling i915/perf version would probably be a justified
versioning interface.

Regards, Joonas

> 
> 
> Thanks,
> 
> 
> -Lionel
> 
> 
> >
> >> ---
> >>   drivers/gpu/drm/i915/i915_perf.c | 17 +++++++++++++++++
> >>   include/uapi/drm/i915_drm.h      | 19 +++++++++++++++++++
> >>   2 files changed, 36 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> >> index da721fce2543..6c98ffa2135e 100644
> >> --- a/drivers/gpu/drm/i915/i915_perf.c
> >> +++ b/drivers/gpu/drm/i915/i915_perf.c
> >> @@ -2433,6 +2433,20 @@ static void i915_perf_disable_locked(struct i915_perf_stream *stream)
> >>                  stream->ops->disable(stream);
> >>   }
> >>   
> >> +/**
> >> + * i915_perf_flush_data - handle `I915_PERF_IOCTL_FLUSH_DATA` ioctl
> >> + * @stream: An enabled i915 perf stream
> >> + *
> >> + * The intention is to flush all the data available for reading from the OA
> >> + * buffer
> >> + */
> >> +static void i915_perf_flush_data(struct i915_perf_stream *stream)
> >> +{
> >> +       struct drm_i915_private *dev_priv = stream->dev_priv;
> >> +
> >> +       dev_priv->perf.oa.pollin = oa_buffer_check(stream->dev_priv, true);
> >> +}
> >> +
> >>   /**
> >>    * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
> >>    * @stream: An i915 perf stream
> >> @@ -2456,6 +2470,9 @@ static long i915_perf_ioctl_locked(struct i915_perf_stream *stream,
> >>          case I915_PERF_IOCTL_DISABLE:
> >>                  i915_perf_disable_locked(stream);
> >>                  return 0;
> >> +       case I915_PERF_IOCTL_FLUSH_DATA:
> >> +               i915_perf_flush_data(stream);
> >> +               return 0;
> >>          }
> >>   
> >>          return -EINVAL;
> >> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> >> index b6db5e544a35..0f0d20080572 100644
> >> --- a/include/uapi/drm/i915_drm.h
> >> +++ b/include/uapi/drm/i915_drm.h
> >> @@ -1594,6 +1594,25 @@ struct drm_i915_perf_open_param {
> >>    */
> >>   #define I915_PERF_IOCTL_DISABLE        _IO('i', 0x1)
> >>   
> >> +/**
> >> + * Actively check the availability of data from a stream.
> >> + *
> >> + * A stream data availability can be driven by two types of events :
> >> + *
> >> + *   - if enabled, the kernel's hrtimer checking the amount of available data
> >> + *     in the OA buffer through head/tail registers.
> >> + *
> >> + *   - if enabled, the OA unit's interrupt mechanism
> >> + *
> >> + * The kernel hrtimer incur a cost of running callback at fixed time
> >> + * intervals, while the OA interrupt might only happen rarely. In the
> >> + * situation where the application has disabled the kernel's hrtimer and only
> >> + * uses the OA interrupt to know about available data, the application can
> >> + * request an active check of the available OA data through this ioctl. This
> >> + * will make any data in the OA buffer available with either poll() or read().
> >> + */
> >> +#define I915_PERF_IOCTL_FLUSH_DATA _IO('i', 0x2)
> >> +
> >>   /**
> >>    * Common to all i915 perf records
> >>    */
> >> -- 
> >> 2.20.1
> >>
> >> _______________________________________________
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> 
>