Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754793AbaGVNpv (ORCPT ); Tue, 22 Jul 2014 09:45:51 -0400 Received: from pegasos-out.vodafone.de ([80.84.1.38]:41391 "EHLO pegasos-out.vodafone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751681AbaGVNpt (ORCPT ); Tue, 22 Jul 2014 09:45:49 -0400 X-Spam-Flag: NO X-Spam-Score: 0.2 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 4218E7252CB X-DKIM: OpenDKIM Filter v2.0.2 smtp-04.vodafone.de 43D1CE5B2C Message-ID: <53CE6AFA.1060807@vodafone.de> Date: Tue, 22 Jul 2014 15:45:30 +0200 From: =?ISO-8859-1?Q?Christian_K=F6nig?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: =?ISO-8859-1?Q?Christian_K=F6nig?= , Dave Airlie , Maarten Lankhorst , Thomas Hellstrom , nouveau , LKML , dri-devel , Ben Skeggs , "Deucher, Alexander" Subject: Re: [Nouveau] [PATCH 09/17] drm/radeon: use common fence implementation for fences References: <20140709093124.11354.3774.stgit@patser> <20140709122953.11354.46381.stgit@patser> <53CE2421.5040906@amd.com> <20140722114607.GL15237@phenom.ffwll.local> <20140722115737.GN15237@phenom.ffwll.local> <53CE56ED.4040109@vodafone.de> <20140722132652.GO15237@phenom.ffwll.local> In-Reply-To: <20140722132652.GO15237@phenom.ffwll.local> 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 22.07.2014 15:26, schrieb Daniel Vetter: > On Tue, Jul 22, 2014 at 02:19:57PM +0200, Christian K?nig wrote: >> Am 22.07.2014 13:57, schrieb Daniel Vetter: >>> On Tue, Jul 22, 2014 at 01:46:07PM +0200, Daniel Vetter wrote: >>>> On Tue, Jul 22, 2014 at 10:43:13AM +0200, Christian K?nig wrote: >>>>> Am 22.07.2014 06:05, schrieb Dave Airlie: >>>>>> On 9 July 2014 22:29, Maarten Lankhorst wrote: >>>>>>> Signed-off-by: Maarten Lankhorst >>>>>>> --- >>>>>>> drivers/gpu/drm/radeon/radeon.h | 15 +- >>>>>>> drivers/gpu/drm/radeon/radeon_device.c | 60 ++++++++- >>>>>>> drivers/gpu/drm/radeon/radeon_fence.c | 223 ++++++++++++++++++++++++++------ >>>>>>> 3 files changed, 248 insertions(+), 50 deletions(-) >>>>>>> >>>>>> From what I can see this is still suffering from the problem that we >>>>>> need to find a proper solution to, >>>>>> >>>>>> My summary of the issues after talking to Jerome and Ben and >>>>>> re-reading things is: >>>>>> >>>>>> We really need to work out a better interface into the drivers to be >>>>>> able to avoid random atomic entrypoints, >>>>> Which is exactly what I criticized from the very first beginning. Good to >>>>> know that I'm not the only one thinking that this isn't such a good idea. >>>> I guess I've lost context a bit, but which atomic entry point are we >>>> talking about? Afaics the only one that's mandatory is the is >>>> fence->signaled callback to check whether a fence really has been >>>> signalled. It's used internally by the fence code to avoid spurious >>>> wakeups. Afaik that should be doable already on any hardware. If that's >>>> not the case then we can always track the signalled state in software and >>>> double-check in a worker thread before updating the sw state. And wrap >>>> this all up into a special fence class if there's more than one driver >>>> needing this. >>> One thing I've forgotten: The i915 scheduler that's floating around runs >>> its bottom half from irq context. So I really want to be able to check >>> fence state from irq context and I also want to make it possible >>> (possible! not mandatory) to register callbacks which are run from any >>> context asap after the fence is signalled. >> NAK, that's just the bad design I've talked about. Checking fence state >> inside the same driver from interrupt context is OK, because it's the >> drivers interrupt that we are talking about here. >> >> Checking fence status from another drivers interrupt context is what really >> concerns me here, cause your driver doesn't have the slightest idea if the >> called driver is really capable of checking the fence right now. > I guess my mail hasn't been clear then. If you don't like it we could add > a bit of glue to insulate the madness and bad design i915 might do from > radeon. That imo doesn't invalidate the overall fence interfaces. > > So what about the following: > - fence->enabling_signaling is restricted to be called from process > context. We don't use any different yet, so would boild down to adding a > WARN_ON(in_interrupt) or so to fence_enable_sw_signalling. > > - Make fence->signaled optional (already the case) and don't implement it > in readon (i.e. reduce this patch here). Only downside is that radeon > needs to correctly (i.e. without races or so) call fence_signal. And the > cross-driver synchronization might be a bit less efficient. Note that > you can call fence_signal from wherever you want to, so hopefully that > doesn't restrict your implementation. > > End result: No one calls into radeon from interrupt context, and this is > guaranteed. > > Would that be something you can agree to? No, the whole enable_signaling stuff should go away. No callback from the driver into the fence code, only the other way around. fence->signaled as well as fence->wait should become mandatory and only called from process context without holding any locks, neither atomic nor any mutex/semaphore (rcu might be ok). > Like I've said I think restricting the insanity other people are willing > to live with just because you don't like it isn't right. But it is > certainly right for you to insist on not being forced into any such > design. I think the above would achieve this. I don't think so. If it's just me I would say that I'm just to cautious and the idea is still save to apply to the whole kernel. But since Dave, Jerome and Ben seems to have similar concerns I think we need to agree to a minimum and save interface for all drivers. Christian. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/