From patchwork Fri Feb 1 01:42:42 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 10791693 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 65DCC14E1 for ; Fri, 1 Feb 2019 01:42:57 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 57ADC31A80 for ; Fri, 1 Feb 2019 01:42:57 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4BC8D31A8E; Fri, 1 Feb 2019 01:42:57 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id C9B2531A80 for ; Fri, 1 Feb 2019 01:42:56 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 988946E239; Fri, 1 Feb 2019 01:42:55 +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 4FEE96E239 for ; Fri, 1 Feb 2019 01:42:54 +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 15423530-1500050 for multiple; Fri, 01 Feb 2019 01:42:42 +0000 From: Chris Wilson To: intel-gfx@lists.freedesktop.org Date: Fri, 1 Feb 2019 01:42:42 +0000 Message-Id: <20190201014242.6022-1-chris@chris-wilson.co.uk> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH] drm/i915: Allow normal clients to always preempt idle priority clients 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" X-Virus-Scanned: ClamAV using ClamSMTP When first enabling preemption, we hesitated from making it a free-for-all where every higher priority client would force a preempt-to-idle cycle and take over from all lower priority clients. We hesitated because we were uncertain just how well preemption would work in practice, whether the preemption latency itself would detract from the latency gains for higher priority tasks and whether it would work at all. Since introducing preemption, we have been enabling it for more common tasks, even giving normal clients a small preemptive boost when they first start (to aide fairness and improve interactivity). Now lets take one step further and give permission for all normal (priority:0) clients to preempt any idle (priority:<0) task so that users running long compute jobs do not overly impact other jobs (i.e. their desktop) and the system remains responsive under such idle loads. References: f6322eddaff7 ("drm/i915/preemption: Allow preemption between submission ports") References: b16c765122f9 ("drm/i915: Priority boost for new clients") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: Michal Wajdeczko Cc: Michał Winiarski Cc: "Bloomfield, Jon" Reviewed-by: Daniele Ceraolo Spurio --- drivers/gpu/drm/i915/intel_ringbuffer.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h index 34d0a148e664..983ad1e7914d 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.h +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h @@ -592,7 +592,20 @@ intel_engine_has_preemption(const struct intel_engine_cs *engine) static inline bool __execlists_need_preempt(int prio, int last) { - return prio > max(0, last); + /* + * Allow preemption of low -> normal -> high, but we do + * not allow low priority tasks to preempt other low priority + * tasks under the impression that latency for low priority + * tasks does not matter (as much as background throughput), + * so kiss. + * + * More naturally we would write + * prio >= max(0, last); + * except that we wish to prevent triggering preemption at the same + * priority level: the task that is running should remain running + * to preserve FIFO ordering of dependencies. + */ + return prio > max(I915_PRIORITY_NORMAL - 1, last); } static inline void