[Intel-gfx] [RFC PATCH 55/97] drm/i915/guc: Update intel_gt_wait_for_idle to work with GuC
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Thu May 27 09:02:55 UTC 2021
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(>->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 = >->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);
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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