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

Matthew Brost matthew.brost at intel.com
Thu May 27 14:37:07 UTC 2021


On Thu, May 27, 2021 at 10:02:55AM +0100, Tvrtko Ursulin wrote:
> 
> On 26/05/2021 19:18, Matthew Brost wrote:
> > On Wed, May 26, 2021 at 10:21:05AM +0100, Tvrtko Ursulin wrote:
> > > 
> > > 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 at intel.com>
> > > > > > Signed-off-by: Matthew Brost <matthew.brost at 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.
> > > 
> > 
> > I just didn't want to add a spin_lock if there is known working code
> > path without one and our code fits into that path. I can add a comment
> > but I don't really think it necessary.
> 
> Lock already exists in the wake_up_all, it is not about adding your own.
> 
> As premature optimisations are usually best avoided it is simply about how
> do you justify a):
> 
> +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);
> 
> When the easy alternative (easy to read, easy to review, easy to maintain)
> is b):
> 
> +static void decr_outstanding_submission_g2h(struct intel_guc *guc)
> +{
> +	if (atomic_dec_and_test(&guc->outstanding_submission_g2h))
> +		wake_up_all(&guc->ct.wq);
> 

I'll go with option B.

Matt

> For me as external reader the question seems to be, I will say it again, is
> the case of no waiters a common one and is this a hot path to justify
> avoiding a function call by adding the mental complexity explained in the
> waitqueue_active comment? Here and in the other places in the GuC backend
> waitqueue_active is used.
> 
> Regards,
> 
> Tvrtko


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