From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0D5B4C352A2 for ; Fri, 7 Feb 2020 09:41:28 +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 D0D34218AC for ; Fri, 7 Feb 2020 09:41:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D0D34218AC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com 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 620BC6FBE8; Fri, 7 Feb 2020 09:41:27 +0000 (UTC) Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by gabe.freedesktop.org (Postfix) with ESMTPS id E64F56FBE8 for ; Fri, 7 Feb 2020 09:41:25 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Feb 2020 01:41:25 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,412,1574150400"; d="scan'208";a="225324637" Received: from gaia.fi.intel.com ([10.237.72.192]) by orsmga008.jf.intel.com with ESMTP; 07 Feb 2020 01:41:24 -0800 Received: by gaia.fi.intel.com (Postfix, from userid 1000) id 2F4805C0D64; Fri, 7 Feb 2020 11:40:29 +0200 (EET) From: Mika Kuoppala To: Chris Wilson , intel-gfx@lists.freedesktop.org In-Reply-To: <158106754158.7306.3828961672199232273@skylake-alporthouse-com> References: <20200206204915.2636606-1-chris@chris-wilson.co.uk> <877e0yahfx.fsf@gaia.fi.intel.com> <158106754158.7306.3828961672199232273@skylake-alporthouse-com> Date: Fri, 07 Feb 2020 11:40:29 +0200 Message-ID: <87zhdu91ma.fsf@gaia.fi.intel.com> MIME-Version: 1.0 Subject: Re: [Intel-gfx] [PATCH 1/4] drm/i915/gt: Prevent queuing retire workers on the virtual engine 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Chris Wilson writes: > Quoting Mika Kuoppala (2020-02-07 09:13:22) >> Chris Wilson writes: >> >> > Virtual engines are fleeting. They carry a reference count and may be freed >> > when their last request is retired. This makes them unsuitable for the >> > task of housing engine->retire.work so assert that it is not used. >> >> There is chicken and egg problem here that I fail to grasp. > > In the general case, an engine may be providing a workqueue for requests > for other engines. That's the conundrum I had in mind when writing that; > if and only if, we have the latest request from that engine on that > retire worker, then it will be protected by the last request (and our > careful ordering of dereferences). That is not guaranteed to be the case > (even for only virtual requests on a virtual engine, as we may not have > the last request queued for retirement, and so it may be retired ahead > of time.) > > So as I write that, it becomes much clearer that there is a lifetime > issue with the concept of retirement queues on the virtual engine. > >> If the retire work is the mechanism which triggers the request >> freeing, then the order should be fine. As the engine is still >> there for last request. > > It's not the only mechanism, so concurrent retirements are expected. Well, it is somewhat embarrassing for me that this is described by the lower half of the commit message... >> Or is the problem that it happens inside the worker which is inside >> the engine? > > The immediate problem is that we didn't even set up the virtual engine to > have retirement queues :) Indeed, there is none. Reviewed-by: Mika Kuoppala _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx