From patchwork Thu Dec 12 14:04:28 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 11288405 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 E2EE513B6 for ; Thu, 12 Dec 2019 14:05:45 +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 CB94621655 for ; Thu, 12 Dec 2019 14:05:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB94621655 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 3BA6D6ED78; Thu, 12 Dec 2019 14:05:40 +0000 (UTC) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from fireflyinternet.com (mail.fireflyinternet.com [109.228.58.192]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0664B6ED71 for ; Thu, 12 Dec 2019 14:05:36 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from haswell.alporthouse.com (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP id 19555629-1500050 for multiple; Thu, 12 Dec 2019 14:04:58 +0000 From: Chris Wilson To: intel-gfx@lists.freedesktop.org Date: Thu, 12 Dec 2019 14:04:28 +0000 Message-Id: <20191212140459.1307617-2-chris@chris-wilson.co.uk> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191212140459.1307617-1-chris@chris-wilson.co.uk> References: <20191212140459.1307617-1-chris@chris-wilson.co.uk> MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH 02/33] drm/i915: Eliminate the trylock for awaiting an earlier request 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: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" We currently use an error-prone mutex_trylock to grab another timeline to find an earlier request along it. However, with a bit of a sleight-of-hand, we can reduce the mutex_trylock to a spin_lock on the immediate request and careful pointer chasing to acquire a reference on the previous request. Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin --- drivers/gpu/drm/i915/i915_request.c | 39 ++++++++++++++++------------- 1 file changed, 21 insertions(+), 18 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index fb8738987aeb..f513747ff027 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -768,34 +768,37 @@ i915_request_create(struct intel_context *ce) static int i915_request_await_start(struct i915_request *rq, struct i915_request *signal) { - struct intel_timeline *tl; struct dma_fence *fence; int err; GEM_BUG_ON(i915_request_timeline(rq) == rcu_access_pointer(signal->timeline)); + fence = NULL; rcu_read_lock(); - tl = rcu_dereference(signal->timeline); - if (i915_request_started(signal) || !kref_get_unless_zero(&tl->kref)) - tl = NULL; - rcu_read_unlock(); - if (!tl) /* already started or maybe even completed */ - return 0; + spin_lock_irq(&signal->lock); + if (!i915_request_started(signal) && + !list_is_first(&signal->link, + &rcu_dereference(signal->timeline)->requests)) { + struct i915_request *prev = list_prev_entry(signal, link); - fence = ERR_PTR(-EAGAIN); - if (mutex_trylock(&tl->mutex)) { - fence = NULL; - if (!i915_request_started(signal) && - !list_is_first(&signal->link, &tl->requests)) { - signal = list_prev_entry(signal, link); - fence = dma_fence_get(&signal->fence); + /* + * Peek at the request before us in the timeline. That + * request will only be valid before it is retired, so + * after acquiring a reference to it, confirm that it is + * still part of the signaler's timeline. + */ + if (i915_request_get_rcu(prev)) { + if (list_next_entry(prev, link) == signal) + fence = &prev->fence; + else + i915_request_put(prev); } - mutex_unlock(&tl->mutex); } - intel_timeline_put(tl); - if (IS_ERR_OR_NULL(fence)) - return PTR_ERR_OR_ZERO(fence); + spin_unlock_irq(&signal->lock); + rcu_read_unlock(); + if (!fence) + return 0; err = 0; if (intel_timeline_sync_is_later(i915_request_timeline(rq), fence))