From patchwork Wed Aug 5 12:21:55 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 11701803 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id DEBB3913 for ; Wed, 5 Aug 2020 12:22:57 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C89A122D03 for ; Wed, 5 Aug 2020 12:22:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C89A122D03 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=chris-wilson.co.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id BA7FF89CBA; Wed, 5 Aug 2020 12:22:50 +0000 (UTC) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from fireflyinternet.com (unknown [77.68.26.236]) by gabe.freedesktop.org (Postfix) with ESMTPS id 09BFD6E573 for ; Wed, 5 Aug 2020 12:22:47 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from build.alporthouse.com (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP id 22039460-1500050 for multiple; Wed, 05 Aug 2020 13:22:30 +0100 From: Chris Wilson To: intel-gfx@lists.freedesktop.org Date: Wed, 5 Aug 2020 13:21:55 +0100 Message-Id: <20200805122231.23313-2-chris@chris-wilson.co.uk> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200805122231.23313-1-chris@chris-wilson.co.uk> References: <20200805122231.23313-1-chris@chris-wilson.co.uk> MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH 01/37] drm/i915/gem: Reduce context termination list iteration guard to RCU X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Chris Wilson Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" As we now protect the timeline list using RCU, we can drop the timeline->mutex for guarding the list iteration during context close, as we are searching for an inflight request. Any new request will see the context is banned and not be submitted. In doing so, pull the checks for a concurrent submission of the request (notably the i915_request_completed()) under the engine spinlock, to fully serialise with __i915_request_submit()). That is in the case of preempt-to-busy where the request may be completed during the __i915_request_submit(), we need to be careful that we sample the request status after serialising so that we don't miss the request the engine is actually submitting. Fixes: 4a3174152147 ("drm/i915/gem: Refine occupancy test in kill_context()") References: d22d2d073ef8 ("drm/i915: Protect i915_request_await_start from early waits") # rcu protection of timeline->requests References: https://gitlab.freedesktop.org/drm/intel/-/issues/1622 Signed-off-by: Chris Wilson Reviewed-by: Tvrtko Ursulin --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 32 ++++++++++++--------- 1 file changed, 19 insertions(+), 13 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index d8cccbab7a51..db893f6c516b 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -439,29 +439,36 @@ static bool __cancel_engine(struct intel_engine_cs *engine) return __reset_engine(engine); } -static struct intel_engine_cs *__active_engine(struct i915_request *rq) +static bool +__active_engine(struct i915_request *rq, struct intel_engine_cs **active) { struct intel_engine_cs *engine, *locked; + bool ret = false; /* * Serialise with __i915_request_submit() so that it sees * is-banned?, or we know the request is already inflight. + * + * Note that rq->engine is unstable, and so we double + * check that we have acquired the lock on the final engine. */ locked = READ_ONCE(rq->engine); spin_lock_irq(&locked->active.lock); while (unlikely(locked != (engine = READ_ONCE(rq->engine)))) { spin_unlock(&locked->active.lock); - spin_lock(&engine->active.lock); locked = engine; + spin_lock(&locked->active.lock); } - engine = NULL; - if (i915_request_is_active(rq) && rq->fence.error != -EIO) - engine = rq->engine; + if (!i915_request_completed(rq)) { + if (i915_request_is_active(rq) && rq->fence.error != -EIO) + *active = locked; + ret = true; + } spin_unlock_irq(&locked->active.lock); - return engine; + return ret; } static struct intel_engine_cs *active_engine(struct intel_context *ce) @@ -472,17 +479,16 @@ static struct intel_engine_cs *active_engine(struct intel_context *ce) if (!ce->timeline) return NULL; - mutex_lock(&ce->timeline->mutex); - list_for_each_entry_reverse(rq, &ce->timeline->requests, link) { - if (i915_request_completed(rq)) - break; + rcu_read_lock(); + list_for_each_entry_rcu(rq, &ce->timeline->requests, link) { + if (i915_request_is_active(rq) && i915_request_completed(rq)) + continue; /* Check with the backend if the request is inflight */ - engine = __active_engine(rq); - if (engine) + if (__active_engine(rq, &engine)) break; } - mutex_unlock(&ce->timeline->mutex); + rcu_read_unlock(); return engine; }