Re: [Intel-gfx] [PATCH 06/27] drm/i915/guc: Take engine PM when a context is pinned with GuC submission

[John Harrison <john.c.harrison@intel.com>]

On 9/9/2021 17:41, Matthew Brost wrote:
> On Thu, Sep 09, 2021 at 03:46:43PM -0700, John Harrison wrote:
>> On 8/20/2021 15:44, Matthew Brost wrote:
>>> Taking a PM reference to prevent intel_gt_wait_for_idle from short
>>> circuiting while a scheduling of user context could be enabled.
>> As with earlier PM patch, needs more explanation of what the problem is and
>> why it is only now a problem.
>>
>>
> Same explaination, will add here.
>
>>> v2:
>>>    (Daniel Vetter)
>>>     - Add might_lock annotations to pin / unpin function
>>>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gt/intel_context.c       |  3 ++
>>>    drivers/gpu/drm/i915/gt/intel_engine_pm.h     | 15 ++++++++
>>>    drivers/gpu/drm/i915/gt/intel_gt_pm.h         | 10 ++++++
>>>    .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 36 +++++++++++++++++--
>>>    drivers/gpu/drm/i915/intel_wakeref.h          | 12 +++++++
>>>    5 files changed, 73 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
>>> index c8595da64ad8..508cfe5770c0 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_context.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
>>> @@ -240,6 +240,8 @@ int __intel_context_do_pin_ww(struct intel_context *ce,
>>>    	if (err)
>>>    		goto err_post_unpin;
>>> +	intel_engine_pm_might_get(ce->engine);
>>> +
>>>    	if (unlikely(intel_context_is_closed(ce))) {
>>>    		err = -ENOENT;
>>>    		goto err_unlock;
>>> @@ -313,6 +315,7 @@ void __intel_context_do_unpin(struct intel_context *ce, int sub)
>>>    		return;
>>>    	CE_TRACE(ce, "unpin\n");
>>> +	intel_engine_pm_might_put(ce->engine);
>>>    	ce->ops->unpin(ce);
>>>    	ce->ops->post_unpin(ce);
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.h b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
>>> index 17a5028ea177..3fe2ae1bcc26 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
>>> @@ -9,6 +9,7 @@
>>>    #include "i915_request.h"
>>>    #include "intel_engine_types.h"
>>>    #include "intel_wakeref.h"
>>> +#include "intel_gt_pm.h"
>>>    static inline bool
>>>    intel_engine_pm_is_awake(const struct intel_engine_cs *engine)
>>> @@ -31,6 +32,13 @@ static inline bool intel_engine_pm_get_if_awake(struct intel_engine_cs *engine)
>>>    	return intel_wakeref_get_if_active(&engine->wakeref);
>>>    }
>>> +static inline void intel_engine_pm_might_get(struct intel_engine_cs *engine)
>>> +{
>>> +	if (!intel_engine_is_virtual(engine))
>>> +		intel_wakeref_might_get(&engine->wakeref);
>> Why doesn't this need to iterate through the physical engines of the virtual
>> engine?
>>
> Yea, technically it should. This is just an annotation though to check
> if we do something horribly wrong in our code. If we use any physical
> engine in our stack this annotation should pop and we can fix it. I just
> don't see what making this 100% correct for virtual engines buys us. If
> you want I can fix this but thinking the more complex we make this
> annotation the less likely it just gets compiled out with lockdep off
> which is what we are aiming for.
But if the annotation is missing a fundamental lock then it is surely 
not actually going to do any good? Not sure if you need to iterate over 
all child engines + parent but it seems like you should be calling 
might_lock() on at least one engine's mutex to feed the lockdep annotation.

John.

> Matt
>
>> John.
>>
>>> +	intel_gt_pm_might_get(engine->gt);
>>> +}
>>> +
>>>    static inline void intel_engine_pm_put(struct intel_engine_cs *engine)
>>>    {
>>>    	intel_wakeref_put(&engine->wakeref);
>>> @@ -52,6 +60,13 @@ static inline void intel_engine_pm_flush(struct intel_engine_cs *engine)
>>>    	intel_wakeref_unlock_wait(&engine->wakeref);
>>>    }
>>> +static inline void intel_engine_pm_might_put(struct intel_engine_cs *engine)
>>> +{
>>> +	if (!intel_engine_is_virtual(engine))
>>> +		intel_wakeref_might_put(&engine->wakeref);
>>> +	intel_gt_pm_might_put(engine->gt);
>>> +}
>>> +
>>>    static inline struct i915_request *
>>>    intel_engine_create_kernel_request(struct intel_engine_cs *engine)
>>>    {
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.h b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
>>> index a17bf0d4592b..3c173033ce23 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
>>> @@ -31,6 +31,11 @@ static inline bool intel_gt_pm_get_if_awake(struct intel_gt *gt)
>>>    	return intel_wakeref_get_if_active(&gt->wakeref);
>>>    }
>>> +static inline void intel_gt_pm_might_get(struct intel_gt *gt)
>>> +{
>>> +	intel_wakeref_might_get(&gt->wakeref);
>>> +}
>>> +
>>>    static inline void intel_gt_pm_put(struct intel_gt *gt)
>>>    {
>>>    	intel_wakeref_put(&gt->wakeref);
>>> @@ -41,6 +46,11 @@ static inline void intel_gt_pm_put_async(struct intel_gt *gt)
>>>    	intel_wakeref_put_async(&gt->wakeref);
>>>    }
>>> +static inline void intel_gt_pm_might_put(struct intel_gt *gt)
>>> +{
>>> +	intel_wakeref_might_put(&gt->wakeref);
>>> +}
>>> +
>>>    #define with_intel_gt_pm(gt, tmp) \
>>>    	for (tmp = 1, intel_gt_pm_get(gt); tmp; \
>>>    	     intel_gt_pm_put(gt), tmp = 0)
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> index dbf919801de2..e0eed70f9b92 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -1550,7 +1550,12 @@ static int guc_context_pre_pin(struct intel_context *ce,
>>>    static int guc_context_pin(struct intel_context *ce, void *vaddr)
>>>    {
>>> -	return __guc_context_pin(ce, ce->engine, vaddr);
>>> +	int ret = __guc_context_pin(ce, ce->engine, vaddr);
>>> +
>>> +	if (likely(!ret && !intel_context_is_barrier(ce)))
>>> +		intel_engine_pm_get(ce->engine);
>>> +
>>> +	return ret;
>>>    }
>>>    static void guc_context_unpin(struct intel_context *ce)
>>> @@ -1559,6 +1564,9 @@ static void guc_context_unpin(struct intel_context *ce)
>>>    	unpin_guc_id(guc, ce);
>>>    	lrc_unpin(ce);
>>> +
>>> +	if (likely(!intel_context_is_barrier(ce)))
>>> +		intel_engine_pm_put_async(ce->engine);
>>>    }
>>>    static void guc_context_post_unpin(struct intel_context *ce)
>>> @@ -2328,8 +2336,30 @@ static int guc_virtual_context_pre_pin(struct intel_context *ce,
>>>    static int guc_virtual_context_pin(struct intel_context *ce, void *vaddr)
>>>    {
>>>    	struct intel_engine_cs *engine = guc_virtual_get_sibling(ce->engine, 0);
>>> +	int ret = __guc_context_pin(ce, engine, vaddr);
>>> +	intel_engine_mask_t tmp, mask = ce->engine->mask;
>>> +
>>> +	if (likely(!ret))
>>> +		for_each_engine_masked(engine, ce->engine->gt, mask, tmp)
>>> +			intel_engine_pm_get(engine);
>>> -	return __guc_context_pin(ce, engine, vaddr);
>>> +	return ret;
>>> +}
>>> +
>>> +static void guc_virtual_context_unpin(struct intel_context *ce)
>>> +{
>>> +	intel_engine_mask_t tmp, mask = ce->engine->mask;
>>> +	struct intel_engine_cs *engine;
>>> +	struct intel_guc *guc = ce_to_guc(ce);
>>> +
>>> +	GEM_BUG_ON(context_enabled(ce));
>>> +	GEM_BUG_ON(intel_context_is_barrier(ce));
>>> +
>>> +	unpin_guc_id(guc, ce);
>>> +	lrc_unpin(ce);
>>> +
>>> +	for_each_engine_masked(engine, ce->engine->gt, mask, tmp)
>>> +		intel_engine_pm_put_async(engine);
>>>    }
>>>    static void guc_virtual_context_enter(struct intel_context *ce)
>>> @@ -2366,7 +2396,7 @@ static const struct intel_context_ops virtual_guc_context_ops = {
>>>    	.pre_pin = guc_virtual_context_pre_pin,
>>>    	.pin = guc_virtual_context_pin,
>>> -	.unpin = guc_context_unpin,
>>> +	.unpin = guc_virtual_context_unpin,
>>>    	.post_unpin = guc_context_post_unpin,
>>>    	.ban = guc_context_ban,
>>> diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
>>> index ef7e6a698e8a..dd530ae028e0 100644
>>> --- a/drivers/gpu/drm/i915/intel_wakeref.h
>>> +++ b/drivers/gpu/drm/i915/intel_wakeref.h
>>> @@ -124,6 +124,12 @@ enum {
>>>    	__INTEL_WAKEREF_PUT_LAST_BIT__
>>>    };
>>> +static inline void
>>> +intel_wakeref_might_get(struct intel_wakeref *wf)
>>> +{
>>> +	might_lock(&wf->mutex);
>>> +}
>>> +
>>>    /**
>>>     * intel_wakeref_put_flags: Release the wakeref
>>>     * @wf: the wakeref
>>> @@ -171,6 +177,12 @@ intel_wakeref_put_delay(struct intel_wakeref *wf, unsigned long delay)
>>>    			    FIELD_PREP(INTEL_WAKEREF_PUT_DELAY, delay));
>>>    }
>>> +static inline void
>>> +intel_wakeref_might_put(struct intel_wakeref *wf)
>>> +{
>>> +	might_lock(&wf->mutex);
>>> +}
>>> +
>>>    /**
>>>     * intel_wakeref_lock: Lock the wakeref (mutex)
>>>     * @wf: the wakeref