Re: [Intel-gfx] [PATCH 1/2] drm/i915/perf: Register sysctl path globally

[Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>]

On 19/12/11 04:39, Tvrtko Ursulin wrote:
> 
> On 11/12/2019 16:31, Tvrtko Ursulin wrote:
> > On 11/12/2019 16:07, Venkata Sandeep Dhanalakota wrote:
> > > We do not require to register the sysctl paths per instance,
> > > so making registration global.
> > > 
> > > Cc: Sudeep Dutt <sudeep.dutt@intel.com>
> > > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Jani Nikula <jani.nikula@intel.com>
> > > Signed-off-by: Venkata Sandeep Dhanalakota
> > > <venkata.s.dhanalakota@intel.com>
> > > ---
> > >   drivers/gpu/drm/i915/i915_perf.c       | 10 ++++++++--
> > >   drivers/gpu/drm/i915/i915_perf_types.h |  1 -
> > >   2 files changed, 8 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_perf.c
> > > b/drivers/gpu/drm/i915/i915_perf.c
> > > index 8d2e37949f46..426d04214a5d 100644
> > > --- a/drivers/gpu/drm/i915/i915_perf.c
> > > +++ b/drivers/gpu/drm/i915/i915_perf.c
> > > @@ -387,6 +387,8 @@ struct i915_oa_config_bo {
> > >       struct i915_vma *vma;
> > >   };
> > > +static struct ctl_table_header *sysctl_header;
> > > +
> > >   static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer
> > > *hrtimer);
> > >   void i915_oa_config_release(struct kref *ref)
> > > @@ -4345,7 +4347,8 @@ void i915_perf_init(struct drm_i915_private *i915)
> > >           oa_sample_rate_hard_limit = 1000 *
> > >               (RUNTIME_INFO(i915)->cs_timestamp_frequency_khz / 2);
> > > -        perf->sysctl_header = register_sysctl_table(dev_root);
> > > +        if (!sysctl_header)
> > > +            sysctl_header = register_sysctl_table(dev_root);
> > >           mutex_init(&perf->metrics_lock);
> > >           idr_init(&perf->metrics_idr);
> > > @@ -4395,7 +4398,10 @@ void i915_perf_fini(struct drm_i915_private *i915)
> > >       idr_for_each(&perf->metrics_idr, destroy_config, perf);
> > >       idr_destroy(&perf->metrics_idr);
> > > -    unregister_sysctl_table(perf->sysctl_header);
> > > +    if (sysctl_header) {
> > > +        unregister_sysctl_table(sysctl_header);
> > > +        sysctl_header = NULL;
> > > +    }
> > 
> > I am not sure if this could be racy with manual unbind from sysfs. Does
> > PCI core serialize for us?
> 
> Actually with two devices you also need to reference count it since you
> don't want removal of the first device to remove the node but last.
> 
Apparently this is not called during module exit, using krefs is
way go to or have some helper which are called during module init/exit.

void i915_perf_sysctl_register() {
	sysctl_header = register_sysctl_table(dev_root);
}

void i915_perf_sysctl_unregister() {
	unregister_sysctl_table(sysctl_header);
}


> > Regards,
> > 
> > Tvrtko
> > 
> > >       memset(&perf->ops, 0, sizeof(perf->ops));
> > >       perf->i915 = NULL;
> > > diff --git a/drivers/gpu/drm/i915/i915_perf_types.h
> > > b/drivers/gpu/drm/i915/i915_perf_types.h
> > > index 74ddc20a0d37..45e581455f5d 100644
> > > --- a/drivers/gpu/drm/i915/i915_perf_types.h
> > > +++ b/drivers/gpu/drm/i915/i915_perf_types.h
> > > @@ -380,7 +380,6 @@ struct i915_perf {
> > >       struct drm_i915_private *i915;
> > >       struct kobject *metrics_kobj;
> > > -    struct ctl_table_header *sysctl_header;
> > >       /*
> > >        * Lock associated with adding/modifying/removing OA configs
> > > 
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