From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754034AbaEOJmk (ORCPT ); Thu, 15 May 2014 05:42:40 -0400 Received: from pegasos-out.vodafone.de ([80.84.1.38]:58471 "EHLO pegasos-out.vodafone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751187AbaEOJmi (ORCPT ); Thu, 15 May 2014 05:42:38 -0400 X-Spam-Flag: NO X-Spam-Score: -0.045 Authentication-Results: rohrpostix2.prod.vfnet.de (amavisd-new); dkim=pass header.i=@vodafone.de X-DKIM: OpenDKIM Filter v2.6.8 pegasos-out.vodafone.de 4699566F636 X-DKIM: OpenDKIM Filter v2.0.2 smtp-04.vodafone.de 22AD6E4E8C Message-ID: <53748BFD.1050608@vodafone.de> Date: Thu, 15 May 2014 11:42:21 +0200 From: =?ISO-8859-1?Q?Christian_K=F6nig?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Maarten Lankhorst , airlied@linux.ie CC: nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences References: <20140514145134.21163.32350.stgit@patser> <20140514145809.21163.64947.stgit@patser> <53738BCC.2070809@vodafone.de> <5374131D.4010906@canonical.com> <53748702.6070606@vodafone.de> <53748AFA.8010109@canonical.com> In-Reply-To: <53748AFA.8010109@canonical.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 15.05.2014 11:38, schrieb Maarten Lankhorst: > op 15-05-14 11:21, Christian König schreef: >> Am 15.05.2014 03:06, schrieb Maarten Lankhorst: >>> op 14-05-14 17:29, Christian König schreef: >>>>> + /* did fence get signaled after we enabled the sw irq? */ >>>>> + if >>>>> (atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq) >= >>>>> fence->seq) { >>>>> + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring); >>>>> + return false; >>>>> + } >>>>> + >>>>> + fence->fence_wake.flags = 0; >>>>> + fence->fence_wake.private = NULL; >>>>> + fence->fence_wake.func = radeon_fence_check_signaled; >>>>> + __add_wait_queue(&fence->rdev->fence_queue, &fence->fence_wake); >>>>> + fence_get(f); >>>> That looks like a race condition to me. The fence needs to be added >>>> to the wait queue before the check, not after. >>>> >>>> Apart from that the whole approach looks like a really bad idea to >>>> me. How for example is lockup detection supposed to happen with this? >>> It's not a race condition because fence_queue.lock is held when this >>> function is called. >> Ah, I see. That's also the reason why you moved the wake_up_all out >> of the processing function. > Correct. :-) >>> Lockup's a bit of a weird problem, the changes wouldn't allow core >>> ttm code to handle the lockup any more, >>> but any driver specific wait code would still handle this. I did >>> this by design, because in future patches the wait >>> function may be called from outside of the radeon driver. The >>> official wait function takes a timeout parameter, >>> so lockups wouldn't be fatal if the timeout is set to something like >>> 30*HZ for example, it would still return >>> and report that the function timed out. >> Timeouts help with the detection of the lockup, but not at all with >> the handling of them. >> >> What we essentially need is a wait callback into the driver that is >> called in non atomic context without any locks held. >> >> This way we can block for the fence to become signaled with a timeout >> and can then also initiate the reset handling if necessary. >> >> The way you designed the interface now means that the driver never >> gets a chance to wait for the hardware to become idle and so never >> has the opportunity to the reset the whole thing. > You could set up a hangcheck timer like intel does, and end up with a > reliable hangcheck detection that doesn't depend on cpu waits. :-) Or > override the default wait function and restore the old behavior. Overriding the default wait function sounds better, please implement it this way. Thanks, Christian. > > ~Maarten >