Re: [Intel-gfx] [RFC PATCH 55/97] drm/i915/guc: Update intel_gt_wait_for_idle to work with GuC

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

On 25/05/2021 18:07, Matthew Brost wrote:
> On Tue, May 25, 2021 at 11:06:00AM +0100, Tvrtko Ursulin wrote:
>>
>> On 06/05/2021 20:14, Matthew Brost wrote:
>>> When running the GuC the GPU can't be considered idle if the GuC still
>>> has contexts pinned. As such, a call has been added in
>>> intel_gt_wait_for_idle to idle the UC and in turn the GuC by waiting for
>>> the number of unpinned contexts to go to zero.
>>>
>>> Cc: John Harrison <john.c.harrison@intel.com>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gem/i915_gem_mman.c      |  3 +-
>>>    drivers/gpu/drm/i915/gt/intel_gt.c            | 18 ++++
>>>    drivers/gpu/drm/i915/gt/intel_gt.h            |  2 +
>>>    drivers/gpu/drm/i915/gt/intel_gt_requests.c   | 22 ++---
>>>    drivers/gpu/drm/i915/gt/intel_gt_requests.h   |  7 +-
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc.h        |  4 +
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c     |  1 +
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h     |  4 +
>>>    .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 91 ++++++++++++++++++-
>>>    drivers/gpu/drm/i915/gt/uc/intel_uc.h         |  5 +
>>>    drivers/gpu/drm/i915/i915_debugfs.c           |  1 +
>>>    drivers/gpu/drm/i915/i915_gem_evict.c         |  1 +
>>>    .../gpu/drm/i915/selftests/igt_live_test.c    |  2 +-
>>>    .../gpu/drm/i915/selftests/mock_gem_device.c  |  3 +-
>>>    14 files changed, 137 insertions(+), 27 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
>>> index 8598a1c78a4c..2f5295c9408d 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
>>> @@ -634,7 +634,8 @@ mmap_offset_attach(struct drm_i915_gem_object *obj,
>>>    		goto insert;
>>>    	/* Attempt to reap some mmap space from dead objects */
>>> -	err = intel_gt_retire_requests_timeout(&i915->gt, MAX_SCHEDULE_TIMEOUT);
>>> +	err = intel_gt_retire_requests_timeout(&i915->gt, MAX_SCHEDULE_TIMEOUT,
>>> +					       NULL);
>>>    	if (err)
>>>    		goto err;
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
>>> index 8d77dcbad059..1742a8561f69 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c
>>> @@ -574,6 +574,24 @@ static void __intel_gt_disable(struct intel_gt *gt)
>>>    	GEM_BUG_ON(intel_gt_pm_is_awake(gt));
>>>    }
>>> +int intel_gt_wait_for_idle(struct intel_gt *gt, long timeout)
>>> +{
>>> +	long rtimeout;
>>> +
>>> +	/* If the device is asleep, we have no requests outstanding */
>>> +	if (!intel_gt_pm_is_awake(gt))
>>> +		return 0;
>>> +
>>> +	while ((timeout = intel_gt_retire_requests_timeout(gt, timeout,
>>> +							   &rtimeout)) > 0) {
>>> +		cond_resched();
>>> +		if (signal_pending(current))
>>> +			return -EINTR;
>>> +	}
>>> +
>>> +	return timeout ? timeout : intel_uc_wait_for_idle(&gt->uc, rtimeout);
>>> +}
>>> +
>>>    int intel_gt_init(struct intel_gt *gt)
>>>    {
>>>    	int err;
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.h b/drivers/gpu/drm/i915/gt/intel_gt.h
>>> index 7ec395cace69..c775043334bf 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt.h
>>> @@ -48,6 +48,8 @@ void intel_gt_driver_release(struct intel_gt *gt);
>>>    void intel_gt_driver_late_release(struct intel_gt *gt);
>>> +int intel_gt_wait_for_idle(struct intel_gt *gt, long timeout);
>>> +
>>>    void intel_gt_check_and_clear_faults(struct intel_gt *gt);
>>>    void intel_gt_clear_error_registers(struct intel_gt *gt,
>>>    				    intel_engine_mask_t engine_mask);
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>>> index 647eca9d867a..c6c702f236fa 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
>>> @@ -13,6 +13,7 @@
>>>    #include "intel_gt_pm.h"
>>>    #include "intel_gt_requests.h"
>>>    #include "intel_timeline.h"
>>> +#include "uc/intel_uc.h"
>>>    static bool retire_requests(struct intel_timeline *tl)
>>>    {
>>> @@ -130,7 +131,8 @@ void intel_engine_fini_retire(struct intel_engine_cs *engine)
>>>    	GEM_BUG_ON(engine->retire);
>>>    }
>>> -long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
>>> +long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout,
>>> +				      long *rtimeout)
>>
>> What is 'rtimeout', I know remaining, but it can be more self-descriptive to
>> start with.
>>
> 
> 'remaining_timeout' it is.
> 
>> It feels a bit churny for what it is. How plausible would be alternatives to
>> either change existing timeout to in/out, or measure sleep internally in
>> this function, or just risk sleeping twice as long by passing the original
>> timeout to uc idle as well?
>>
> 
> Originally had it just passing in the same value, got review feedback
> saying I should pass in the adjusted value. Hard to make everyone happy.

Ok.

>   
>>>    {
>>>    	struct intel_gt_timelines *timelines = &gt->timelines;
>>>    	struct intel_timeline *tl, *tn;
>>> @@ -195,22 +197,10 @@ out_active:	spin_lock(&timelines->lock);
>>>    	if (flush_submission(gt, timeout)) /* Wait, there's more! */
>>>    		active_count++;
>>> -	return active_count ? timeout : 0;
>>> -}
>>> -
>>> -int intel_gt_wait_for_idle(struct intel_gt *gt, long timeout)
>>> -{
>>> -	/* If the device is asleep, we have no requests outstanding */
>>> -	if (!intel_gt_pm_is_awake(gt))
>>> -		return 0;
>>> -
>>> -	while ((timeout = intel_gt_retire_requests_timeout(gt, timeout)) > 0) {
>>> -		cond_resched();
>>> -		if (signal_pending(current))
>>> -			return -EINTR;
>>> -	}
>>> +	if (rtimeout)
>>> +		*rtimeout = timeout;
>>> -	return timeout;
>>> +	return active_count ? timeout : 0;
>>>    }
>>>    static void retire_work_handler(struct work_struct *work)
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.h b/drivers/gpu/drm/i915/gt/intel_gt_requests.h
>>> index fcc30a6e4fe9..4419787124e2 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.h
>>> @@ -10,10 +10,11 @@ struct intel_engine_cs;
>>>    struct intel_gt;
>>>    struct intel_timeline;
>>> -long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout);
>>> +long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout,
>>> +				      long *rtimeout);
>>>    static inline void intel_gt_retire_requests(struct intel_gt *gt)
>>>    {
>>> -	intel_gt_retire_requests_timeout(gt, 0);
>>> +	intel_gt_retire_requests_timeout(gt, 0, NULL);
>>>    }
>>>    void intel_engine_init_retire(struct intel_engine_cs *engine);
>>> @@ -21,8 +22,6 @@ void intel_engine_add_retire(struct intel_engine_cs *engine,
>>>    			     struct intel_timeline *tl);
>>>    void intel_engine_fini_retire(struct intel_engine_cs *engine);
>>> -int intel_gt_wait_for_idle(struct intel_gt *gt, long timeout);
>>> -
>>>    void intel_gt_init_requests(struct intel_gt *gt);
>>>    void intel_gt_park_requests(struct intel_gt *gt);
>>>    void intel_gt_unpark_requests(struct intel_gt *gt);
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> index 485e98f3f304..47eaa69809e8 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> @@ -38,6 +38,8 @@ struct intel_guc {
>>>    	spinlock_t irq_lock;
>>>    	unsigned int msg_enabled_mask;
>>> +	atomic_t outstanding_submission_g2h;
>>> +
>>>    	struct {
>>>    		bool enabled;
>>>    		void (*reset)(struct intel_guc *guc);
>>> @@ -239,6 +241,8 @@ static inline void intel_guc_disable_msg(struct intel_guc *guc, u32 mask)
>>>    	spin_unlock_irq(&guc->irq_lock);
>>>    }
>>> +int intel_guc_wait_for_idle(struct intel_guc *guc, long timeout);
>>> +
>>>    int intel_guc_reset_engine(struct intel_guc *guc,
>>>    			   struct intel_engine_cs *engine);
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> index f1893030ca88..cf701056fa14 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> @@ -111,6 +111,7 @@ void intel_guc_ct_init_early(struct intel_guc_ct *ct)
>>>    	INIT_LIST_HEAD(&ct->requests.incoming);
>>>    	INIT_WORK(&ct->requests.worker, ct_incoming_request_worker_func);
>>>    	tasklet_init(&ct->receive_tasklet, ct_receive_tasklet_func, (unsigned long)ct);
>>> +	init_waitqueue_head(&ct->wq);
>>>    }
>>>    static inline const char *guc_ct_buffer_type_to_str(u32 type)
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>>> index 660bf37238e2..ab1b79ab960b 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>>> @@ -10,6 +10,7 @@
>>>    #include <linux/spinlock.h>
>>>    #include <linux/workqueue.h>
>>>    #include <linux/ktime.h>
>>> +#include <linux/wait.h>
>>>    #include "intel_guc_fwif.h"
>>> @@ -68,6 +69,9 @@ struct intel_guc_ct {
>>>    	struct tasklet_struct receive_tasklet;
>>> +	/** @wq: wait queue for g2h chanenl */
>>> +	wait_queue_head_t wq;
>>> +
>>>    	struct {
>>>    		u16 last_fence; /* last fence used to send request */
>>> 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 ae0b386467e3..0ff7dd6d337d 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -253,6 +253,74 @@ static inline void set_lrc_desc_registered(struct intel_guc *guc, u32 id,
>>>    	xa_store_irq(&guc->context_lookup, id, ce, GFP_ATOMIC);
>>>    }
>>> +static int guc_submission_busy_loop(struct intel_guc* guc,
>>> +				    const u32 *action,
>>> +				    u32 len,
>>> +				    u32 g2h_len_dw,
>>> +				    bool loop)
>>> +{
>>> +	int err;
>>> +
>>> +	err = intel_guc_send_busy_loop(guc, action, len, g2h_len_dw, loop);
>>> +
>>> +	if (!err && g2h_len_dw)
>>> +		atomic_inc(&guc->outstanding_submission_g2h);
>>> +
>>> +	return err;
>>> +}
>>> +
>>> +static int guc_wait_for_pending_msg(struct intel_guc *guc,
>>> +				    atomic_t *wait_var,
>>> +				    bool interruptible,
>>> +				    long timeout)
>>> +{
>>> +	const int state = interruptible ?
>>> +		TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
>>> +	DEFINE_WAIT(wait);
>>> +
>>> +	might_sleep();
>>> +	GEM_BUG_ON(timeout < 0);
>>> +
>>> +	if (!atomic_read(wait_var))
>>> +		return 0;
>>> +
>>> +	if (!timeout)
>>> +		return -ETIME;
>>> +
>>> +	for (;;) {
>>> +		prepare_to_wait(&guc->ct.wq, &wait, state);
>>> +
>>> +		if (!atomic_read(wait_var))
>>> +			break;
>>> +
>>> +		if (signal_pending_state(state, current)) {
>>> +			timeout = -ERESTARTSYS;
>>> +			break;
>>> +		}
>>> +
>>> +		if (!timeout) {
>>> +			timeout = -ETIME;
>>> +			break;
>>> +		}
>>> +
>>> +		timeout = io_schedule_timeout(timeout);
>>> +	}
>>> +	finish_wait(&guc->ct.wq, &wait);
>>> +
>>> +	return (timeout < 0) ? timeout : 0;
>>> +}
>>
>> See if it is possible to simplify all this with wait_var_event and
>> wake_up_var.
>>
> 
> Let me check on that.
>   
>>> +
>>> +int intel_guc_wait_for_idle(struct intel_guc *guc, long timeout)
>>> +{
>>> +	bool interruptible = true;
>>> +
>>> +	if (unlikely(timeout < 0))
>>> +		timeout = -timeout, interruptible = false;
>>> +
>>> +	return guc_wait_for_pending_msg(guc, &guc->outstanding_submission_g2h,
>>> +					interruptible, timeout);
>>> +}
>>> +
>>>    static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>>>    {
>>>    	int err;
>>> @@ -279,6 +347,7 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>>>    	err = intel_guc_send_nb(guc, action, len, g2h_len_dw);
>>>    	if (!enabled && !err) {
>>> +		atomic_inc(&guc->outstanding_submission_g2h);
>>>    		set_context_enabled(ce);
>>>    	} else if (!enabled) {
>>>    		clr_context_pending_enable(ce);
>>> @@ -734,7 +803,7 @@ static int __guc_action_register_context(struct intel_guc *guc,
>>>    		offset,
>>>    	};
>>> -	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), 0, true);
>>> +	return guc_submission_busy_loop(guc, action, ARRAY_SIZE(action), 0, true);
>>>    }
>>>    static int register_context(struct intel_context *ce)
>>> @@ -754,7 +823,7 @@ static int __guc_action_deregister_context(struct intel_guc *guc,
>>>    		guc_id,
>>>    	};
>>> -	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action),
>>> +	return guc_submission_busy_loop(guc, action, ARRAY_SIZE(action),
>>>    					G2H_LEN_DW_DEREGISTER_CONTEXT, true);
>>>    }
>>> @@ -871,7 +940,9 @@ static int guc_context_pin(struct intel_context *ce, void *vaddr)
>>>    static void guc_context_unpin(struct intel_context *ce)
>>>    {
>>> -	unpin_guc_id(ce_to_guc(ce), ce);
>>> +	struct intel_guc *guc = ce_to_guc(ce);
>>> +
>>> +	unpin_guc_id(guc, ce);
>>>    	lrc_unpin(ce);
>>>    }
>>> @@ -894,7 +965,7 @@ static void __guc_context_sched_disable(struct intel_guc *guc,
>>>    	intel_context_get(ce);
>>> -	intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action),
>>> +	guc_submission_busy_loop(guc, action, ARRAY_SIZE(action),
>>>    				 G2H_LEN_DW_SCHED_CONTEXT_MODE_SET, true);
>>>    }
>>> @@ -1437,6 +1508,15 @@ g2h_context_lookup(struct intel_guc *guc, u32 desc_idx)
>>>    	return ce;
>>>    }
>>> +static void decr_outstanding_submission_g2h(struct intel_guc *guc)
>>> +{
>>> +	if (atomic_dec_and_test(&guc->outstanding_submission_g2h)) {
>>> +		smp_mb();
>>> +		if (waitqueue_active(&guc->ct.wq))
>>> +			wake_up_all(&guc->ct.wq);
>>
>> I keep pointing out this pattern is racy and at least needs comment why it
>> is safe.
>>
> 
> There is a comment in wake queue code header saying why this is safe. I
> don't think we need to repeat this here.

Yeah, _describing how to make it safe_, after it starts with:

  * NOTE: this function is lockless and requires care, incorrect usage _will_
  * lead to sporadic and non-obvious failure.

Then it also says:

  * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
  * which (when the lock is uncontended) are of roughly equal cost.

I question the need to optimize this path since it means reader has to figure out if it is safe while a simple wake_up_all after atomic_dec_and_test would have done it.

Is the case of no waiters a predominant one? It at least deserves a comment explaining why the optimisation is important.

Regards,

Tvrtko

> 
> Matt
> 
>> Regards,
>>
>> Tvrtko
>>
>>> +	}
>>> +}
>>> +
>>>    int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
>>>    					  const u32 *msg,
>>>    					  u32 len)
>>> @@ -1472,6 +1552,8 @@ int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
>>>    		lrc_destroy(&ce->ref);
>>>    	}
>>> +	decr_outstanding_submission_g2h(guc);
>>> +
>>>    	return 0;
>>>    }
>>> @@ -1520,6 +1602,7 @@ int intel_guc_sched_done_process_msg(struct intel_guc *guc,
>>>    		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>>>    	}
>>> +	decr_outstanding_submission_g2h(guc);
>>>    	intel_context_put(ce);
>>>    	return 0;
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.h b/drivers/gpu/drm/i915/gt/uc/intel_uc.h
>>> index 9c954c589edf..c4cef885e984 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.h
>>> @@ -81,6 +81,11 @@ uc_state_checkers(guc, guc_submission);
>>>    #undef uc_state_checkers
>>>    #undef __uc_state_checker
>>> +static inline int intel_uc_wait_for_idle(struct intel_uc *uc, long timeout)
>>> +{
>>> +	return intel_guc_wait_for_idle(&uc->guc, timeout);
>>> +}
>>> +
>>>    #define intel_uc_ops_function(_NAME, _OPS, _TYPE, _RET) \
>>>    static inline _TYPE intel_uc_##_NAME(struct intel_uc *uc) \
>>>    { \
>>> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
>>> index 8dd374691102..bb29838d1cd7 100644
>>> --- a/drivers/gpu/drm/i915/i915_debugfs.c
>>> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
>>> @@ -36,6 +36,7 @@
>>>    #include "gt/intel_gt_clock_utils.h"
>>>    #include "gt/intel_gt.h"
>>>    #include "gt/intel_gt_pm.h"
>>> +#include "gt/intel_gt.h"
>>>    #include "gt/intel_gt_requests.h"
>>>    #include "gt/intel_reset.h"
>>>    #include "gt/intel_rc6.h"
>>> diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
>>> index 4d2d59a9942b..2b73ddb11c66 100644
>>> --- a/drivers/gpu/drm/i915/i915_gem_evict.c
>>> +++ b/drivers/gpu/drm/i915/i915_gem_evict.c
>>> @@ -27,6 +27,7 @@
>>>     */
>>>    #include "gem/i915_gem_context.h"
>>> +#include "gt/intel_gt.h"
>>>    #include "gt/intel_gt_requests.h"
>>>    #include "i915_drv.h"
>>> diff --git a/drivers/gpu/drm/i915/selftests/igt_live_test.c b/drivers/gpu/drm/i915/selftests/igt_live_test.c
>>> index c130010a7033..1c721542e277 100644
>>> --- a/drivers/gpu/drm/i915/selftests/igt_live_test.c
>>> +++ b/drivers/gpu/drm/i915/selftests/igt_live_test.c
>>> @@ -5,7 +5,7 @@
>>>     */
>>>    #include "i915_drv.h"
>>> -#include "gt/intel_gt_requests.h"
>>> +#include "gt/intel_gt.h"
>>>    #include "../i915_selftest.h"
>>>    #include "igt_flush_test.h"
>>> diff --git a/drivers/gpu/drm/i915/selftests/mock_gem_device.c b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
>>> index cf40004bc92a..6c06816e2b99 100644
>>> --- a/drivers/gpu/drm/i915/selftests/mock_gem_device.c
>>> +++ b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
>>> @@ -51,7 +51,8 @@ void mock_device_flush(struct drm_i915_private *i915)
>>>    	do {
>>>    		for_each_engine(engine, gt, id)
>>>    			mock_engine_flush(engine);
>>> -	} while (intel_gt_retire_requests_timeout(gt, MAX_SCHEDULE_TIMEOUT));
>>> +	} while (intel_gt_retire_requests_timeout(gt, MAX_SCHEDULE_TIMEOUT,
>>> +						  NULL));
>>>    }
>>>    static void mock_device_release(struct drm_device *dev)
>>>