From patchwork Wed Jan 6 11:09:53 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 7967471 Return-Path: X-Original-To: patchwork-dri-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id A89079F1CC for ; Wed, 6 Jan 2016 11:10:16 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 1D453201C8 for ; Wed, 6 Jan 2016 11:10:12 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id EEA1A20173 for ; Wed, 6 Jan 2016 11:10:09 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 600D56E302; Wed, 6 Jan 2016 03:10:08 -0800 (PST) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by gabe.freedesktop.org (Postfix) with ESMTPS id 483726E302; Wed, 6 Jan 2016 03:10:07 -0800 (PST) Received: by mail-wm0-f53.google.com with SMTP id l65so55269642wmf.1; Wed, 06 Jan 2016 03:10:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:mime-version:content-type :content-transfer-encoding; bh=F7Q9NWF+ZH3hgWf59G3uBWYKOXprlQkFbtb3uZfh7yM=; b=vF+58G1E7glH+1W8ld3p9DOzrUAaTH0ir8HDxC1q4QsRL955fF/9C3uoLGBWq09Fa4 bg/B0Ytb8WhU8xjVBCwTbNUlPOe7mBvqahU0z2MFsv1JCKksxp/vEjRiRv1YElAtG6+m BaSZmnD8Ihhad4X6023O1ZKaQMTDTndcqAHt2hPJfmsI/B9m8xgiN5zIkC5bQfXHCX2a u2m5sNjjl+uEht25xIhr802yrqIIxjhp4fS3+qv/9fjhO/xO7nEw6fST8mH5XaQO2zqD clF7PHs2yV402SzX6PTofEPN4ABcWmIBA21DJipwneo6e/GTqQToRy/rctIG4rDV2G2s 6E+A== X-Received: by 10.194.209.129 with SMTP id mm1mr69408879wjc.47.1452078605400; Wed, 06 Jan 2016 03:10:05 -0800 (PST) Received: from haswell.alporthouse.com ([78.156.65.138]) by smtp.gmail.com with ESMTPSA id n129sm8171364wmb.1.2016.01.06.03.10.03 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 06 Jan 2016 03:10:04 -0800 (PST) From: Chris Wilson To: dri-devel@lists.freedesktop.org Subject: [PATCH 1/3] drm: Defer disabling the vblank IRQ until the next interrupt (for instant-off) Date: Wed, 6 Jan 2016 11:09:53 +0000 Message-Id: <1452078595-2840-1-git-send-email-chris@chris-wilson.co.uk> X-Mailer: git-send-email 2.7.0.rc3 MIME-Version: 1.0 Cc: =?UTF-8?q?Michel=20D=C3=A4nzer?= , Laurent Pinchart , Dave Airlie , intel-gfx@lists.freedesktop.org X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Spam-Status: No, score=-4.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,RP_MATCHES_RCVD,T_DKIM_INVALID,UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On vblank instant-off systems, we can get into a situation where the cost of enabling and disabling the vblank IRQ around a drmWaitVblank query dominates. And with the advent of even deeper hardware sleep state, touching registers becomes ever more expensive. However, we know that if the user wants the current vblank counter, they are also very likely to immediately queue a vblank wait and so we can keep the interrupt around and only turn it off if we have no further vblank requests queued within the interrupt interval. After vblank event delivery, this patch adds a shadow of one vblank where the interrupt is kept alive for the user to query and queue another vblank event. Similarly, if the user is using blocking drmWaitVblanks, the interrupt will be disabled on the IRQ following the wait completion. However, if the user is simply querying the current vblank counter and timestamp, the interrupt will be disabled after every IRQ and the user will enabled it again on the first query following the IRQ. v2: Mario Kleiner - After testing this, one more thing that would make sense is to move the disable block at the end of drm_handle_vblank() instead of at the top. Turns out that if high precision timestaming is disabled or doesn't work for some reason (as can be simulated by echo 0 > /sys/module/drm/parameters/timestamp_precision_usec), then with your delayed disable code at its current place, the vblank counter won't increment anymore at all for instant queries, ie. with your other "instant query" patches. Clients which repeatedly query the counter and wait for it to progress will simply hang, spinning in an endless query loop. There's that comment in vblank_disable_and_save: "* Skip this step if there isn't any high precision timestamp * available. In that case we can't account for this and just * hope for the best. */ With the disable happening after leading edge of vblank (== hw counter increment already happened) but before the vblank counter/timestamp handling in drm_handle_vblank, that step is needed to keep the counter progressing, so skipping it is bad. Now without high precision timestamping support, a kms driver must not set dev->vblank_disable_immediate = true, as this would cause problems for clients, so this shouldn't matter, but it would be good to still make this robust against a future kms driver which might have unreliable high precision timestamping, e.g., high precision timestamping that intermittently doesn't work. v3: Patch before coffee needs extra coffee. Testcase: igt/kms_vblank Signed-off-by: Chris Wilson Cc: Ville Syrjälä Cc: Daniel Vetter Cc: Michel Dänzer Cc: Laurent Pinchart Cc: Dave Airlie , Cc: Mario Kleiner --- drivers/gpu/drm/drm_irq.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 607f493ae801..ca5ef87c57c1 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -1213,9 +1213,9 @@ void drm_vblank_put(struct drm_device *dev, unsigned int pipe) if (atomic_dec_and_test(&vblank->refcount)) { if (drm_vblank_offdelay == 0) return; - else if (dev->vblank_disable_immediate || drm_vblank_offdelay < 0) + else if (drm_vblank_offdelay < 0) vblank_disable_fn((unsigned long)vblank); - else + else if (!dev->vblank_disable_immediate) mod_timer(&vblank->disable_timer, jiffies + ((drm_vblank_offdelay * HZ)/1000)); } @@ -1835,6 +1835,16 @@ bool drm_handle_vblank(struct drm_device *dev, unsigned int pipe) wake_up(&vblank->queue); drm_handle_vblank_events(dev, pipe); + /* With instant-off, we defer disabling the interrupt until after + * we finish processing the following vblank. The disable has to + * be last (after drm_handle_vblank_events) so that the timestamp + * is always accurate. + */ + if (dev->vblank_disable_immediate && + drm_vblank_offdelay > 0 && + !atomic_read(&vblank->refcount)) + vblank_disable_fn((unsigned long)vblank); + spin_unlock_irqrestore(&dev->event_lock, irqflags); return true;