From patchwork Fri Sep 20 08:36:24 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 11154057 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 9FCFA14DB for ; Fri, 20 Sep 2019 08:37:04 +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 87E1D2070C for ; Fri, 20 Sep 2019 08:37:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87E1D2070C 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 6218F6E821; Fri, 20 Sep 2019 08:37:03 +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 4DF076E821 for ; Fri, 20 Sep 2019 08:37:02 +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 18555085-1500050 for multiple; Fri, 20 Sep 2019 09:36:26 +0100 From: Chris Wilson To: intel-gfx@lists.freedesktop.org Date: Fri, 20 Sep 2019 09:36:24 +0100 Message-Id: <20190920083624.4601-1-chris@chris-wilson.co.uk> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH] drm/i915: Prevent bonded requests from overtaking each other on preemption X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.23 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" Force bonded requests to run on distinct engines so that they cannot be shuffled onto the same engine where timeslicing will reverse the order. A bonded request will often wait on a semaphore signaled by its master, creating an implicit dependency -- if we ignore that implicit dependency and allow the bonded request to run on the same engine and before its master, we will cause a GPU hang. We can prevent this inversion by restricting which engines we allow ourselves to jump to upon preemption, i.e. baking in the arrangement established at first execution. (We should also consider capturing the implicit dependency using i915_sched_add_dependency(), but first we need to think about the constraints that requires on the execution/retirement ordering.) Fixes: 8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing") References: ee1136908e9b ("drm/i915/execlists: Virtual engine bonding") Signed-off-by: Chris Wilson Cc: Mika Kuoppala Cc: Tvrtko Ursulin Reviewed-by: Tvrtko Ursulin --- drivers/gpu/drm/i915/gt/intel_lrc.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index a99166a2d2eb..7920649e4d87 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -3755,18 +3755,21 @@ static void virtual_bond_execute(struct i915_request *rq, struct dma_fence *signal) { struct virtual_engine *ve = to_virtual_engine(rq->engine); + intel_engine_mask_t allowed, exec; struct ve_bond *bond; bond = virtual_find_bond(ve, to_request(signal)->engine); - if (bond) { - intel_engine_mask_t old, new, cmp; + if (!bond) + return; - cmp = READ_ONCE(rq->execution_mask); - do { - old = cmp; - new = cmp & bond->sibling_mask; - } while ((cmp = cmpxchg(&rq->execution_mask, old, new)) != old); - } + /* Restrict the bonded request to run on only the slaved engines */ + allowed = bond->sibling_mask & ~to_request(signal)->engine->mask; + exec = READ_ONCE(rq->execution_mask); + while (!try_cmpxchg(&rq->execution_mask, &exec, exec & allowed)) + ; + + /* Prevent the master from being re-run on the slaved engines */ + to_request(signal)->execution_mask &= ~allowed; } struct intel_context *