From 27af5eea54d161e1636001a7f2b5efd3b7a3d1f9 Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin Date: Mon, 4 Apr 2016 12:11:56 +0100 Subject: [PATCH] drm/i915: Move execlists irq handler to a bottom half Doing a lot of work in the interrupt handler introduces huge latencies to the system as a whole. Most dramatic effect can be seen by running an all engine stress test like igt/gem_exec_nop/all where, when the kernel config is lean enough, the whole system can be brought into multi-second periods of complete non-interactivty. That can look for example like this: NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [kworker/u8:3:143] Modules linked in: [redacted for brevity] CPU: 0 PID: 143 Comm: kworker/u8:3 Tainted: G U L 4.5.0-160321+ #183 Hardware name: Intel Corporation Broadwell Client platform/WhiteTip Mountain 1 Workqueue: i915 gen6_pm_rps_work [i915] task: ffff8800aae88000 ti: ffff8800aae90000 task.ti: ffff8800aae90000 RIP: 0010:[] [] __do_softirq+0x72/0x1d0 RSP: 0000:ffff88014f403f38 EFLAGS: 00000206 RAX: ffff8800aae94000 RBX: 0000000000000000 RCX: 00000000000006e0 RDX: 0000000000000020 RSI: 0000000004208060 RDI: 0000000000215d80 RBP: ffff88014f403f80 R08: 0000000b1b42c180 R09: 0000000000000022 R10: 0000000000000004 R11: 00000000ffffffff R12: 000000000000a030 R13: 0000000000000082 R14: ffff8800aa4d0080 R15: 0000000000000082 FS: 0000000000000000(0000) GS:ffff88014f400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa53b90c000 CR3: 0000000001a0a000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: 042080601b33869f ffff8800aae94000 00000000fffc2678 ffff88010000000a 0000000000000000 000000000000a030 0000000000005302 ffff8800aa4d0080 0000000000000206 ffff88014f403f90 ffffffff8104a716 ffff88014f403fa8 Call Trace: [] irq_exit+0x86/0x90 [] smp_apic_timer_interrupt+0x3d/0x50 [] apic_timer_interrupt+0x7c/0x90 [] ? gen8_write64+0x1a0/0x1a0 [i915] [] ? _raw_spin_unlock_irqrestore+0x9/0x20 [] gen8_write32+0x104/0x1a0 [i915] [] ? n_tty_receive_buf_common+0x372/0xae0 [] gen6_set_rps_thresholds+0x1be/0x330 [i915] [] gen6_set_rps+0x70/0x200 [i915] [] intel_set_rps+0x25/0x30 [i915] [] gen6_pm_rps_work+0x10d/0x2e0 [i915] [] ? finish_task_switch+0x72/0x1c0 [] process_one_work+0x139/0x350 [] worker_thread+0x126/0x490 [] ? rescuer_thread+0x320/0x320 [] kthread+0xc4/0xe0 [] ? kthread_create_on_node+0x170/0x170 [] ret_from_fork+0x3f/0x70 [] ? kthread_create_on_node+0x170/0x170 I could not explain, or find a code path, which would explain a +20 second lockup, but from some instrumentation it was apparent the interrupts off proportion of time was between 10-25% under heavy load which is quite bad. When a interrupt "cliff" is reached, which was >~320k irq/s on my machine, the whole system goes into a terrible state of the above described multi-second lockups. By moving the GT interrupt handling to a tasklet in a most simple way, the problem above disappears completely. Testing the effect on sytem-wide latencies using igt/gem_syslatency shows the following before this patch: gem_syslatency: cycles=1532739, latency mean=416531.829us max=2499237us gem_syslatency: cycles=1839434, latency mean=1458099.157us max=4998944us gem_syslatency: cycles=1432570, latency mean=2688.451us max=1201185us gem_syslatency: cycles=1533543, latency mean=416520.499us max=2498886us This shows that the unrelated process is experiencing huge delays in its wake-up latency. After the patch the results look like this: gem_syslatency: cycles=808907, latency mean=53.133us max=1640us gem_syslatency: cycles=862154, latency mean=62.778us max=2117us gem_syslatency: cycles=856039, latency mean=58.079us max=2123us gem_syslatency: cycles=841683, latency mean=56.914us max=1667us Showing a huge improvement in the unrelated process wake-up latency. It also shows an approximate halving in the number of total empty batches submitted during the test. This may not be worrying since the test puts the driver under a very unrealistic load with ncpu threads doing empty batch submission to all GPU engines each. Another benefit compared to the hard-irq handling is that now work on all engines can be dispatched in parallel since we can have up to number of CPUs active tasklets. (While previously a single hard-irq would serially dispatch on one engine after another.) More interesting scenario with regards to throughput is "gem_latency -n 100" which shows 25% better throughput and CPU usage, and 14% better dispatch latencies. I did not find any gains or regressions with Synmark2 or GLbench under light testing. More benchmarking is certainly required. v2: * execlists_lock should be taken as spin_lock_bh when queuing work from userspace now. (Chris Wilson) * uncore.lock must be taken with spin_lock_irq when submitting requests since that now runs from either softirq or process context. v3: * Expanded commit message with more testing data; * converted missed locking sites to _bh; * added execlist_lock comment. (Chris Wilson) v4: * Mention dispatch parallelism in commit. (Chris Wilson) * Do not hold uncore.lock over MMIO reads since the block is already serialised per-engine via the tasklet itself. (Chris Wilson) * intel_lrc_irq_handler should be static. (Chris Wilson) * Cancel/sync the tasklet on GPU reset. (Chris Wilson) * Document and WARN that tasklet cannot be active/pending on engine cleanup. (Chris Wilson/Imre Deak) Signed-off-by: Tvrtko Ursulin Cc: Chris Wilson Cc: Imre Deak Testcase: igt/gem_exec_nop/all Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94350 Reviewed-by: Chris Wilson Link: http://patchwork.freedesktop.org/patch/msgid/1459768316-6670-1-git-send-email-tvrtko.ursulin@linux.intel.com --- drivers/gpu/drm/i915/i915_debugfs.c | 5 ++-- drivers/gpu/drm/i915/i915_gem.c | 10 ++++--- drivers/gpu/drm/i915/i915_irq.c | 2 +- drivers/gpu/drm/i915/intel_lrc.c | 36 +++++++++++++++---------- drivers/gpu/drm/i915/intel_lrc.h | 1 - drivers/gpu/drm/i915/intel_ringbuffer.h | 3 ++- 6 files changed, 33 insertions(+), 24 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c index 0b25228c202e..a2e3af02c292 100644 --- a/drivers/gpu/drm/i915/i915_debugfs.c +++ b/drivers/gpu/drm/i915/i915_debugfs.c @@ -2100,7 +2100,6 @@ static int i915_execlists(struct seq_file *m, void *data) for_each_engine(engine, dev_priv) { struct drm_i915_gem_request *head_req = NULL; int count = 0; - unsigned long flags; seq_printf(m, "%s\n", engine->name); @@ -2127,13 +2126,13 @@ static int i915_execlists(struct seq_file *m, void *data) i, status, ctx_id); } - spin_lock_irqsave(&engine->execlist_lock, flags); + spin_lock_bh(&engine->execlist_lock); list_for_each(cursor, &engine->execlist_queue) count++; head_req = list_first_entry_or_null(&engine->execlist_queue, struct drm_i915_gem_request, execlist_link); - spin_unlock_irqrestore(&engine->execlist_lock, flags); + spin_unlock_bh(&engine->execlist_lock); seq_printf(m, "\t%d requests in queue\n", count); if (head_req) { diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index ca96fc12cdf4..40f90c7e718a 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2842,13 +2842,15 @@ static void i915_gem_reset_engine_cleanup(struct drm_i915_private *dev_priv, */ if (i915.enable_execlists) { - spin_lock_irq(&engine->execlist_lock); + /* Ensure irq handler finishes or is cancelled. */ + tasklet_kill(&engine->irq_tasklet); + spin_lock_bh(&engine->execlist_lock); /* list_splice_tail_init checks for empty lists */ list_splice_tail_init(&engine->execlist_queue, &engine->execlist_retired_req_list); + spin_unlock_bh(&engine->execlist_lock); - spin_unlock_irq(&engine->execlist_lock); intel_execlists_retire_requests(engine); } @@ -2968,9 +2970,9 @@ i915_gem_retire_requests(struct drm_device *dev) i915_gem_retire_requests_ring(engine); idle &= list_empty(&engine->request_list); if (i915.enable_execlists) { - spin_lock_irq(&engine->execlist_lock); + spin_lock_bh(&engine->execlist_lock); idle &= list_empty(&engine->execlist_queue); - spin_unlock_irq(&engine->execlist_lock); + spin_unlock_bh(&engine->execlist_lock); intel_execlists_retire_requests(engine); } diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index a9c18137e3f5..c85eb8dec2dc 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -1323,7 +1323,7 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift) if (iir & (GT_RENDER_USER_INTERRUPT << test_shift)) notify_ring(engine); if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift)) - intel_lrc_irq_handler(engine); + tasklet_schedule(&engine->irq_tasklet); } static irqreturn_t gen8_gt_irq_handler(struct drm_i915_private *dev_priv, diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c index 5d4ca3b11ae2..a1db6a02cf23 100644 --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -131,6 +131,7 @@ * preemption, but just sampling the new tail pointer). * */ +#include #include #include @@ -418,20 +419,18 @@ static void execlists_submit_requests(struct drm_i915_gem_request *rq0, { struct drm_i915_private *dev_priv = rq0->i915; - /* BUG_ON(!irqs_disabled()); */ - execlists_update_context(rq0); if (rq1) execlists_update_context(rq1); - spin_lock(&dev_priv->uncore.lock); + spin_lock_irq(&dev_priv->uncore.lock); intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL); execlists_elsp_write(rq0, rq1); intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL); - spin_unlock(&dev_priv->uncore.lock); + spin_unlock_irq(&dev_priv->uncore.lock); } static void execlists_context_unqueue(struct intel_engine_cs *engine) @@ -538,13 +537,14 @@ get_context_status(struct intel_engine_cs *engine, unsigned int read_pointer, /** * intel_lrc_irq_handler() - handle Context Switch interrupts - * @ring: Engine Command Streamer to handle. + * @engine: Engine Command Streamer to handle. * * Check the unread Context Status Buffers and manage the submission of new * contexts to the ELSP accordingly. */ -void intel_lrc_irq_handler(struct intel_engine_cs *engine) +static void intel_lrc_irq_handler(unsigned long data) { + struct intel_engine_cs *engine = (struct intel_engine_cs *)data; struct drm_i915_private *dev_priv = engine->dev->dev_private; u32 status_pointer; unsigned int read_pointer, write_pointer; @@ -552,8 +552,7 @@ void intel_lrc_irq_handler(struct intel_engine_cs *engine) unsigned int csb_read = 0, i; unsigned int submit_contexts = 0; - spin_lock(&dev_priv->uncore.lock); - intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL); + intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL); status_pointer = I915_READ_FW(RING_CONTEXT_STATUS_PTR(engine)); @@ -578,8 +577,7 @@ void intel_lrc_irq_handler(struct intel_engine_cs *engine) _MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, engine->next_context_status_buffer << 8)); - intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL); - spin_unlock(&dev_priv->uncore.lock); + intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL); spin_lock(&engine->execlist_lock); @@ -621,7 +619,7 @@ static void execlists_context_queue(struct drm_i915_gem_request *request) i915_gem_request_reference(request); - spin_lock_irq(&engine->execlist_lock); + spin_lock_bh(&engine->execlist_lock); list_for_each_entry(cursor, &engine->execlist_queue, execlist_link) if (++num_elements > 2) @@ -646,7 +644,7 @@ static void execlists_context_queue(struct drm_i915_gem_request *request) if (num_elements == 0) execlists_context_unqueue(engine); - spin_unlock_irq(&engine->execlist_lock); + spin_unlock_bh(&engine->execlist_lock); } static int logical_ring_invalidate_all_caches(struct drm_i915_gem_request *req) @@ -1033,9 +1031,9 @@ void intel_execlists_retire_requests(struct intel_engine_cs *engine) return; INIT_LIST_HEAD(&retired_list); - spin_lock_irq(&engine->execlist_lock); + spin_lock_bh(&engine->execlist_lock); list_replace_init(&engine->execlist_retired_req_list, &retired_list); - spin_unlock_irq(&engine->execlist_lock); + spin_unlock_bh(&engine->execlist_lock); list_for_each_entry_safe(req, tmp, &retired_list, execlist_link) { struct intel_context *ctx = req->ctx; @@ -2016,6 +2014,13 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *engine) if (!intel_engine_initialized(engine)) return; + /* + * Tasklet cannot be active at this point due intel_mark_active/idle + * so this is just for documentation. + */ + if (WARN_ON(test_bit(TASKLET_STATE_SCHED, &engine->irq_tasklet.state))) + tasklet_kill(&engine->irq_tasklet); + dev_priv = engine->dev->dev_private; if (engine->buffer) { @@ -2089,6 +2094,9 @@ logical_ring_init(struct drm_device *dev, struct intel_engine_cs *engine) INIT_LIST_HEAD(&engine->execlist_retired_req_list); spin_lock_init(&engine->execlist_lock); + tasklet_init(&engine->irq_tasklet, + intel_lrc_irq_handler, (unsigned long)engine); + logical_ring_init_platform_invariants(engine); ret = i915_cmd_parser_init_ring(engine); diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h index a17cb12221ba..0b0853eee91e 100644 --- a/drivers/gpu/drm/i915/intel_lrc.h +++ b/drivers/gpu/drm/i915/intel_lrc.h @@ -118,7 +118,6 @@ int intel_execlists_submission(struct i915_execbuffer_params *params, struct drm_i915_gem_execbuffer2 *args, struct list_head *vmas); -void intel_lrc_irq_handler(struct intel_engine_cs *engine); void intel_execlists_retire_requests(struct intel_engine_cs *engine); #endif /* _INTEL_LRC_H_ */ diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h index 221a94627aab..18074ab55f61 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.h +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h @@ -266,7 +266,8 @@ struct intel_engine_cs { } semaphore; /* Execlists */ - spinlock_t execlist_lock; + struct tasklet_struct irq_tasklet; + spinlock_t execlist_lock; /* used inside tasklet, use spin_lock_bh */ struct list_head execlist_queue; struct list_head execlist_retired_req_list; unsigned int next_context_status_buffer; -- 2.20.1