As we funnel more and more contexts into the breadcrumbs on an engine, the hold time of b->irq_lock grows. As we may then contend with the b->irq_lock during request submission, this increases the burden upon the engine->active.lock and so directly impacts both our execution latency and client latency. If we split the b->irq_lock by introducing a per-context spinlock to manage the signalers within a context, we then only need the b->irq_lock for enabling/disabling the interrupt and can avoid taking the lock for walking the list of contexts within the signal worker. Even with the current setup, this greatly reduces the number of times we have to take and fight for b->irq_lock. Furthermore, this closes the race between enabling the signaling context while it is in the process of being signaled and removed: <4>[ 416.208555] list_add corruption. prev->next should be next (ffff8881951d5910), but was dead000000000100. (prev=ffff8882781bb870). <4>[ 416.208573] WARNING: CPU: 7 PID: 0 at lib/list_debug.c:28 __list_add_valid+0x4d/0x70 <4>[ 416.208575] Modules linked in: i915(+) vgem snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio mei_hdcp x86_pkg_temp_thermal coretemp ax88179_178a usbnet mii crct10dif_pclmul snd_intel_dspcfg crc32_pclmul snd_hda_codec snd_hwdep ghash_clmulni_intel snd_hda_core e1000e snd_pcm ptp pps_core mei_me mei prime_numbers intel_lpss_pci [last unloaded: i915] <4>[ 416.208611] CPU: 7 PID: 0 Comm: swapper/7 Tainted: G U 5.8.0-CI-CI_DRM_8852+ #1 <4>[ 416.208614] Hardware name: Intel Corporation Ice Lake Client Platform/IceLake Y LPDDR4x T4 RVP TLC, BIOS ICLSFWR1.R00.3212.A00.1905212112 05/21/2019 <4>[ 416.208627] RIP: 0010:__list_add_valid+0x4d/0x70 <4>[ 416.208631] Code: c3 48 89 d1 48 c7 c7 60 18 33 82 48 89 c2 e8 ea e0 b6 ff 0f 0b 31 c0 c3 48 89 c1 4c 89 c6 48 c7 c7 b0 18 33 82 e8 d3 e0 b6 ff <0f> 0b 31 c0 c3 48 89 f2 4c 89 c1 48 89 fe 48 c7 c7 00 19 33 82 e8 <4>[ 416.208633] RSP: 0018:ffffc90000280e18 EFLAGS: 00010086 <4>[ 416.208636] RAX: 0000000000000000 RBX: ffff888250a44880 RCX: 0000000000000105 <4>[ 416.208639] RDX: 0000000000000105 RSI: ffffffff82320c5b RDI: 00000000ffffffff <4>[ 416.208641] RBP: ffff8882781bb870 R08: 0000000000000000 R09: 0000000000000001 <4>[ 416.208643] R10: 00000000054d2957 R11: 000000006abbd991 R12: ffff8881951d58c8 <4>[ 416.208646] R13: ffff888286073880 R14: ffff888286073848 R15: ffff8881951d5910 <4>[ 416.208669] FS: 0000000000000000(0000) GS:ffff88829c180000(0000) knlGS:0000000000000000 <4>[ 416.208671] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 <4>[ 416.208673] CR2: 0000556231326c48 CR3: 0000000005610001 CR4: 0000000000760ee0 <4>[ 416.208675] PKRU: 55555554 <4>[ 416.208677] Call Trace: <4>[ 416.208679] <IRQ> <4>[ 416.208751] i915_request_enable_breadcrumb+0x278/0x400 [i915] <4>[ 416.208839] __i915_request_submit+0xca/0x2a0 [i915] <4>[ 416.208892] __execlists_submission_tasklet+0x480/0x1830 [i915] <4>[ 416.208942] execlists_submission_tasklet+0xc4/0x130 [i915] <4>[ 416.208947] tasklet_action_common.isra.17+0x6c/0x1c0 <4>[ 416.208954] __do_softirq+0xdf/0x498 <4>[ 416.208960] ? handle_fasteoi_irq+0x150/0x150 <4>[ 416.208964] asm_call_on_stack+0xf/0x20 <4>[ 416.208966] </IRQ> <4>[ 416.208969] do_softirq_own_stack+0xa1/0xc0 <4>[ 416.208972] irq_exit_rcu+0xb5/0xc0 <4>[ 416.208976] common_interrupt+0xf7/0x260 <4>[ 416.208980] asm_common_interrupt+0x1e/0x40 <4>[ 416.208985] RIP: 0010:cpuidle_enter_state+0xb6/0x410 <4>[ 416.208987] Code: 00 31 ff e8 9c 3e 89 ff 80 7c 24 0b 00 74 12 9c 58 f6 c4 02 0f 85 31 03 00 00 31 ff e8 e3 6c 90 ff e8 fe a4 94 ff fb 45 85 ed <0f> 88 c7 02 00 00 49 63 c5 4c 2b 24 24 48 8d 14 40 48 8d 14 90 48 <4>[ 416.208989] RSP: 0018:ffffc90000143e70 EFLAGS: 00000206 <4>[ 416.208991] RAX: 0000000000000007 RBX: ffffe8ffffda8070 RCX: 0000000000000000 <4>[ 416.208993] RDX: 0000000000000000 RSI: ffffffff8238b4ee RDI: ffffffff8233184f <4>[ 416.208995] RBP: ffffffff826b4e00 R08: 0000000000000000 R09: 0000000000000000 <4>[ 416.208997] R10: 0000000000000001 R11: 0000000000000000 R12: 00000060e7f24a8f <4>[ 416.208998] R13: 0000000000000003 R14: 0000000000000003 R15: 0000000000000003 <4>[ 416.209012] cpuidle_enter+0x24/0x40 <4>[ 416.209016] do_idle+0x22f/0x2d0 <4>[ 416.209022] cpu_startup_entry+0x14/0x20 <4>[ 416.209025] start_secondary+0x158/0x1a0 <4>[ 416.209030] secondary_startup_64+0xa4/0xb0 <4>[ 416.209039] irq event stamp: 10186977 <4>[ 416.209042] hardirqs last enabled at (10186976): [<ffffffff810b9363>] tasklet_action_common.isra.17+0xe3/0x1c0 <4>[ 416.209044] hardirqs last disabled at (10186977): [<ffffffff81a5e5ed>] _raw_spin_lock_irqsave+0xd/0x50 <4>[ 416.209047] softirqs last enabled at (10186968): [<ffffffff810b9a1a>] irq_enter_rcu+0x6a/0x70 <4>[ 416.209049] softirqs last disabled at (10186969): [<ffffffff81c00f4f>] asm_call_on_stack+0xf/0x20 <4>[ 416.209317] list_del corruption, ffff8882781bb870->next is LIST_POISON1 (dead000000000100) <4>[ 416.209317] WARNING: CPU: 7 PID: 46 at lib/list_debug.c:47 __list_del_entry_valid+0x4e/0x90 <4>[ 416.209317] Modules linked in: i915(+) vgem snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio mei_hdcp x86_pkg_temp_thermal coretemp ax88179_178a usbnet mii crct10dif_pclmul snd_intel_dspcfg crc32_pclmul snd_hda_codec snd_hwdep ghash_clmulni_intel snd_hda_core e1000e snd_pcm ptp pps_core mei_me mei prime_numbers intel_lpss_pci [last unloaded: i915] <4>[ 416.209317] CPU: 7 PID: 46 Comm: ksoftirqd/7 Tainted: G U W 5.8.0-CI-CI_DRM_8852+ #1 <4>[ 416.209317] Hardware name: Intel Corporation Ice Lake Client Platform/IceLake Y LPDDR4x T4 RVP TLC, BIOS ICLSFWR1.R00.3212.A00.1905212112 05/21/2019 <4>[ 416.209317] RIP: 0010:__list_del_entry_valid+0x4e/0x90 <4>[ 416.209317] Code: 2e 48 8b 32 48 39 fe 75 3a 48 8b 50 08 48 39 f2 75 48 b8 01 00 00 00 c3 48 89 fe 48 89 c2 48 c7 c7 38 19 33 82 e8 62 e0 b6 ff <0f> 0b 31 c0 c3 48 89 fe 48 c7 c7 70 19 33 82 e8 4e e0 b6 ff 0f 0b <4>[ 416.209317] RSP: 0018:ffffc90000280de8 EFLAGS: 00010086 <4>[ 416.209317] RAX: 0000000000000000 RBX: ffff8882781bb848 RCX: 0000000000010104 <4>[ 416.209317] RDX: 0000000000010104 RSI: ffffffff8238b4ee RDI: 00000000ffffffff <4>[ 416.209317] RBP: ffff8882781bb880 R08: 0000000000000000 R09: 0000000000000001 <4>[ 416.209317] R10: 000000009fb6666e R11: 00000000feca9427 R12: ffffc90000280e18 <4>[ 416.209317] R13: ffff8881951d5930 R14: dead0000000000d8 R15: ffff8882781bb880 <4>[ 416.209317] FS: 0000000000000000(0000) GS:ffff88829c180000(0000) knlGS:0000000000000000 <4>[ 416.209317] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 <4>[ 416.209317] CR2: 0000556231326c48 CR3: 0000000005610001 CR4: 0000000000760ee0 <4>[ 416.209317] PKRU: 55555554 <4>[ 416.209317] Call Trace: <4>[ 416.209317] <IRQ> <4>[ 416.209317] remove_signaling_context.isra.13+0xd/0x70 [i915] <4>[ 416.209513] signal_irq_work+0x1f7/0x4b0 [i915] This is caused by virtual engines where although we take the breadcrumb lock on each of the active engines, they may be different engines on different requests, It turns out that the b->irq_lock was not a sufficient proxy for the engine->active.lock in the case of more than one request, so introduce an explicit lock around ce->signals. Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2276 Fixes: f94343d0a622 ("drm/i915: Remove requirement for holding i915_request.lock for breadcrumbs") Fixes: bda4d4db6dd6 ("drm/i915/gt: Replace intel_engine_transfer_stale_breadcrumbs") Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> --- drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 173 +++++++++++------- .../gpu/drm/i915/gt/intel_breadcrumbs_types.h | 6 +- drivers/gpu/drm/i915/gt/intel_context.c | 3 +- drivers/gpu/drm/i915/gt/intel_context_types.h | 9 +- 4 files changed, 114 insertions(+), 77 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c index a077ef3d02b4..e28efc1bb41d 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c @@ -101,18 +101,27 @@ static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b) intel_gt_pm_put_async(b->irq_engine->gt); } +static void intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b) +{ + spin_lock(&b->irq_lock); + if (b->irq_armed) + __intel_breadcrumbs_disarm_irq(b); + spin_unlock(&b->irq_lock); +} + static void add_signaling_context(struct intel_breadcrumbs *b, struct intel_context *ce) { - intel_context_get(ce); - list_add_tail(&ce->signal_link, &b->signalers); + lockdep_assert_held(&b->signalers_lock); + list_add_rcu(&ce->signal_link, &b->signalers); } static void remove_signaling_context(struct intel_breadcrumbs *b, struct intel_context *ce) { - list_del(&ce->signal_link); - intel_context_put(ce); + spin_lock(&b->signalers_lock); + list_del_rcu(&ce->signal_link); + spin_unlock(&b->signalers_lock); } static inline bool __request_completed(const struct i915_request *rq) @@ -195,15 +204,12 @@ static void signal_irq_work(struct irq_work *work) struct intel_breadcrumbs *b = container_of(work, typeof(*b), irq_work); const ktime_t timestamp = ktime_get(); struct llist_node *signal, *sn; - struct intel_context *ce, *cn; - struct list_head *pos, *next; + struct intel_context *ce; signal = NULL; if (unlikely(!llist_empty(&b->signaled_requests))) signal = llist_del_all(&b->signaled_requests); - spin_lock(&b->irq_lock); - /* * Keep the irq armed until the interrupt after all listeners are gone. * @@ -230,10 +236,32 @@ static void signal_irq_work(struct irq_work *work) * like powertop. */ if (!signal && b->irq_armed && list_empty(&b->signalers)) - __intel_breadcrumbs_disarm_irq(b); + intel_breadcrumbs_disarm_irq(b); + + rcu_read_lock(); + list_for_each_entry_rcu(ce, &b->signalers, signal_link) { + struct list_head *pos, *next; + bool release = false; + + /* + * Since the signal_irq_worker may in fact be running on + * different cores simultaneously, just skip over the other + * thread if it is in the middle of processing the signals. + * We will then advance to the next context, and the other + * core will then skip over us, splitting the work between + * the multiple cores that just happen to processing the + * worker simultaneously. + * + * The other use of ce->signal_lock to add new requests + * to be signaled will always kick the worker afterwards + * ensuring that ce->signals will always be processed at + * least once (even after being skipped). + */ + if (!spin_trylock(&ce->signal_lock)) + continue; - list_for_each_entry_safe(ce, cn, &b->signalers, signal_link) { - GEM_BUG_ON(list_empty(&ce->signals)); + if (list_empty(&ce->signals)) + goto unlock; list_for_each_safe(pos, next, &ce->signals) { struct i915_request *rq = @@ -265,11 +293,16 @@ static void signal_irq_work(struct irq_work *work) if (&ce->signals == pos) { /* now empty */ add_retire(b, ce->timeline); remove_signaling_context(b, ce); + release = true; } } - } - spin_unlock(&b->irq_lock); +unlock: + spin_unlock(&ce->signal_lock); + if (release) + intel_context_put(ce); + } + rcu_read_unlock(); llist_for_each_safe(signal, sn, signal) { struct i915_request *rq = @@ -298,14 +331,15 @@ intel_breadcrumbs_create(struct intel_engine_cs *irq_engine) if (!b) return NULL; - spin_lock_init(&b->irq_lock); + b->irq_engine = irq_engine; + + spin_lock_init(&b->signalers_lock); INIT_LIST_HEAD(&b->signalers); init_llist_head(&b->signaled_requests); + spin_lock_init(&b->irq_lock); init_irq_work(&b->irq_work, signal_irq_work); - b->irq_engine = irq_engine; - return b; } @@ -344,9 +378,9 @@ void intel_breadcrumbs_free(struct intel_breadcrumbs *b) kfree(b); } -static void insert_breadcrumb(struct i915_request *rq, - struct intel_breadcrumbs *b) +static void insert_breadcrumb(struct i915_request *rq) { + struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs; struct intel_context *ce = rq->context; struct list_head *pos; @@ -368,7 +402,33 @@ static void insert_breadcrumb(struct i915_request *rq, } if (list_empty(&ce->signals)) { + /* + * rq->engine is locked by rq->engine->active.lock. That + * however is not known until after rq->engine has been + * dereferenced and the lock acquired. Hence we acquire the + * lock and then validate that rq->engine still matches the + * lock we hold for it. + * + * Here, we are using the breadcrumb lock as a proxy for the + * rq->engine->active.lock, and we know that since the + * breadcrumb will be serialised within i915_request_submit + * the engine cannot change while active as long as we hold + * the breadcrumb lock on that engine. + * + * From the dma_fence_enable_signaling() path, we are outside + * of the request submit/unsubmit path, and so we must be more + * careful to acquire the right lock. + */ + intel_context_get(ce); + spin_lock(&b->signalers_lock); + while (unlikely(b != READ_ONCE(rq->engine)->breadcrumbs)) { + spin_unlock(&b->signalers_lock); + b = READ_ONCE(rq->engine)->breadcrumbs; + spin_lock(&b->signalers_lock); + } add_signaling_context(b, ce); + spin_unlock(&b->signalers_lock); + pos = &ce->signals; } else { /* @@ -407,7 +467,7 @@ static void insert_breadcrumb(struct i915_request *rq, bool i915_request_enable_breadcrumb(struct i915_request *rq) { - struct intel_breadcrumbs *b; + struct intel_context *ce = rq->context; /* Serialises with i915_request_retire() using rq->lock */ if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags)) @@ -422,67 +482,37 @@ bool i915_request_enable_breadcrumb(struct i915_request *rq) if (!test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags)) return true; - /* - * rq->engine is locked by rq->engine->active.lock. That however - * is not known until after rq->engine has been dereferenced and - * the lock acquired. Hence we acquire the lock and then validate - * that rq->engine still matches the lock we hold for it. - * - * Here, we are using the breadcrumb lock as a proxy for the - * rq->engine->active.lock, and we know that since the breadcrumb - * will be serialised within i915_request_submit/i915_request_unsubmit, - * the engine cannot change while active as long as we hold the - * breadcrumb lock on that engine. - * - * From the dma_fence_enable_signaling() path, we are outside of the - * request submit/unsubmit path, and so we must be more careful to - * acquire the right lock. - */ - b = READ_ONCE(rq->engine)->breadcrumbs; - spin_lock(&b->irq_lock); - while (unlikely(b != READ_ONCE(rq->engine)->breadcrumbs)) { - spin_unlock(&b->irq_lock); - b = READ_ONCE(rq->engine)->breadcrumbs; - spin_lock(&b->irq_lock); - } - - /* - * Now that we are finally serialised with request submit/unsubmit, - * [with b->irq_lock] and with i915_request_retire() [via checking - * SIGNALED with rq->lock] confirm the request is indeed active. If - * it is no longer active, the breadcrumb will be attached upon - * i915_request_submit(). - */ + spin_lock(&ce->signal_lock); if (test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags)) - insert_breadcrumb(rq, b); - - spin_unlock(&b->irq_lock); + insert_breadcrumb(rq); + spin_unlock(&ce->signal_lock); return true; } void i915_request_cancel_breadcrumb(struct i915_request *rq) { - struct intel_breadcrumbs *b = rq->engine->breadcrumbs; + struct intel_context *ce = rq->context; + bool release = false; - /* - * We must wait for b->irq_lock so that we know the interrupt handler - * has released its reference to the intel_context and has completed - * the DMA_FENCE_FLAG_SIGNALED_BIT/I915_FENCE_FLAG_SIGNAL dance (if - * required). - */ - spin_lock(&b->irq_lock); + if (!test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags)) + return; + + spin_lock(&ce->signal_lock); if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags)) { - struct intel_context *ce = rq->context; + clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags); list_del(&rq->signal_link); - if (list_empty(&ce->signals)) - remove_signaling_context(b, ce); + if (list_empty(&ce->signals)) { + remove_signaling_context(rq->engine->breadcrumbs, ce); + release = true; + } - clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags); i915_request_put(rq); } - spin_unlock(&b->irq_lock); + spin_unlock(&ce->signal_lock); + if (release) + intel_context_put(ce); } static void print_signals(struct intel_breadcrumbs *b, struct drm_printer *p) @@ -492,18 +522,19 @@ static void print_signals(struct intel_breadcrumbs *b, struct drm_printer *p) drm_printf(p, "Signals:\n"); - spin_lock_irq(&b->irq_lock); - list_for_each_entry(ce, &b->signalers, signal_link) { - list_for_each_entry(rq, &ce->signals, signal_link) { + rcu_read_lock(); + list_for_each_entry_rcu(ce, &b->signalers, signal_link) { + spin_lock_irq(&ce->signal_lock); + list_for_each_entry(rq, &ce->signals, signal_link) drm_printf(p, "\t[%llx:%llx%s] @ %dms\n", rq->fence.context, rq->fence.seqno, i915_request_completed(rq) ? "!" : i915_request_started(rq) ? "*" : "", jiffies_to_msecs(jiffies - rq->emitted_jiffies)); - } + spin_unlock_irq(&ce->signal_lock); } - spin_unlock_irq(&b->irq_lock); + rcu_read_unlock(); } void intel_engine_print_breadcrumbs(struct intel_engine_cs *engine, diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h index 3fa19820b37a..a74bb3062bd8 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h @@ -29,18 +29,16 @@ * the overhead of waking that client is much preferred. */ struct intel_breadcrumbs { - spinlock_t irq_lock; /* protects the lists used in hardirq context */ - /* Not all breadcrumbs are attached to physical HW */ struct intel_engine_cs *irq_engine; + spinlock_t signalers_lock; /* protects the list of signalers */ struct list_head signalers; struct llist_head signaled_requests; + spinlock_t irq_lock; /* protects the interrupt from hardirq context */ struct irq_work irq_work; /* for use from inside irq_lock */ - unsigned int irq_enabled; - bool irq_armed; }; diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c index 8eebb31c6c28..b202dceeb4ec 100644 --- a/drivers/gpu/drm/i915/gt/intel_context.c +++ b/drivers/gpu/drm/i915/gt/intel_context.c @@ -302,7 +302,8 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine) ce->vm = i915_vm_get(engine->gt->vm); - INIT_LIST_HEAD(&ce->signal_link); + /* NB ce->signal_link is used under RCU */ + spin_lock_init(&ce->signal_lock); INIT_LIST_HEAD(&ce->signals); atomic_set(&ce->pin_count, 0); diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h index 18622f1a0249..edb50cbc0eb3 100644 --- a/drivers/gpu/drm/i915/gt/intel_context_types.h +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h @@ -57,7 +57,14 @@ struct intel_context { struct i915_address_space *vm; struct i915_gem_context __rcu *gem_context; - struct list_head signal_link; + /* + * @signal_lock protects the list of requests that need signaling, + * @signals. While there are any requests that need signaling, + * we add the context to the breadcrumbs worker, and remove it + * upon completion/cancellation of the last request. + */ + spinlock_t signal_lock; + struct list_head signal_link; /* Accessed under RCU */ struct list_head signals; struct i915_vma *state; -- 2.20.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
