From: Maarten Lankhorst <maarten.lankhorst@canonical.com>
To: "Christian König" <deathsimple@vodafone.de>,
"Christian König" <christian.koenig@amd.com>,
"Dave Airlie" <airlied@gmail.com>,
"Thomas Hellstrom" <thellstrom@vmware.com>,
nouveau <nouveau@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
"Ben Skeggs" <bskeggs@redhat.com>,
"Deucher, Alexander" <alexander.deucher@amd.com>
Subject: Re: [Nouveau] [PATCH 09/17] drm/radeon: use common fence implementation for fences
Date: Tue, 22 Jul 2014 16:44:16 +0200 [thread overview]
Message-ID: <53CE78C0.9030408@canonical.com> (raw)
In-Reply-To: <53CE6AFA.1060807@vodafone.de>
op 22-07-14 15:45, Christian König schreef:
> Am 22.07.2014 15:26, schrieb Daniel Vetter:
>> On Tue, Jul 22, 2014 at 02:19:57PM +0200, Christian König 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 König wrote:
>>>>>> Am 22.07.2014 06:05, schrieb Dave Airlie:
>>>>>>> On 9 July 2014 22:29, Maarten Lankhorst <maarten.lankhorst@canonical.com> wrote:
>>>>>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
>>>>>>>> ---
>>>>>>>> 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).
fence->wait is mandatory, and already requires sleeping.
If .signaled is not implemented there is no guarantee the fence will be
signaled sometime soon, this is also why enable_signaling exists, to
allow the driver to flush. I get it that it doesn't apply to radeon and nouveau,
but for other drivers that could be necessary, like vmwgfx.
Ironically that is also a part of the ttm fence, except it was called flush there.
I would also like to note that ttm_bo_wait currently is also a function that currently uses is_signaled from atomic_context...
For the more complicated locking worries: Lockdep is your friend, use PROVE_LOCKING and find bugs before they trigger. ;-)
>> 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.
>
next prev parent reply other threads:[~2014-07-22 14:44 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-09 12:29 [PATCH 00/17] Convert TTM to the new fence interface Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 01/17] drm/ttm: add interruptible parameter to ttm_eu_reserve_buffers Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 02/17] drm/ttm: kill off some members to ttm_validate_buffer Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 03/17] drm/nouveau: add reservation to nouveau_gem_ioctl_cpu_prep Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 04/17] drm/nouveau: require reservations for nouveau_fence_sync and nouveau_bo_fence Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 05/17] drm/ttm: call ttm_bo_wait while inside a reservation Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 06/17] drm/ttm: kill fence_lock Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 07/17] drm/nouveau: rework to new fence interface Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 08/17] drm/radeon: add timeout argument to radeon_fence_wait_seq Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 09/17] drm/radeon: use common fence implementation for fences Maarten Lankhorst
2014-07-09 12:57 ` Deucher, Alexander
2014-07-09 13:23 ` [PATCH v2 " Maarten Lankhorst
2014-07-10 17:27 ` Alex Deucher
2014-07-22 4:05 ` [PATCH " Dave Airlie
2014-07-22 8:43 ` Christian König
2014-07-22 11:46 ` Daniel Vetter
2014-07-22 11:52 ` Daniel Vetter
2014-07-22 11:57 ` Daniel Vetter
2014-07-22 12:19 ` Christian König
2014-07-22 13:26 ` [Nouveau] " Daniel Vetter
2014-07-22 13:45 ` Christian König
2014-07-22 14:44 ` Maarten Lankhorst [this message]
2014-07-22 15:02 ` Christian König
2014-07-22 15:18 ` Maarten Lankhorst
2014-07-22 15:17 ` Daniel Vetter
2014-07-22 15:35 ` Christian König
2014-07-22 15:42 ` Daniel Vetter
2014-07-22 15:59 ` Christian König
2014-07-22 16:21 ` Daniel Vetter
2014-07-22 16:39 ` Christian König
2014-07-22 16:52 ` Daniel Vetter
2014-07-22 16:43 ` Daniel Vetter
2014-07-23 6:40 ` Maarten Lankhorst
2014-07-23 6:52 ` Christian König
2014-07-23 7:02 ` Daniel Vetter
2014-07-23 7:06 ` Maarten Lankhorst
2014-07-23 7:09 ` Daniel Vetter
2014-07-23 7:15 ` Christian König
2014-07-23 7:32 ` Maarten Lankhorst
2014-07-23 7:41 ` Christian König
2014-07-23 7:26 ` Christian König
2014-07-23 7:31 ` Daniel Vetter
2014-07-23 7:37 ` Christian König
2014-07-23 7:51 ` Maarten Lankhorst
2014-07-23 7:58 ` Christian König
2014-07-23 8:07 ` Daniel Vetter
2014-07-23 8:20 ` Christian König
2014-07-23 8:25 ` Maarten Lankhorst
2014-07-23 8:42 ` Daniel Vetter
2014-07-23 8:46 ` Christian König
2014-07-23 8:54 ` Daniel Vetter
2014-07-23 9:27 ` Christian König
2014-07-23 9:30 ` Daniel Vetter
2014-07-23 9:36 ` Christian König
2014-07-23 9:38 ` Maarten Lankhorst
2014-07-23 9:39 ` Christian König
2014-07-23 9:39 ` Daniel Vetter
2014-07-23 9:44 ` Daniel Vetter
2014-07-23 9:47 ` Christian König
2014-07-23 9:52 ` Daniel Vetter
2014-07-23 9:55 ` Maarten Lankhorst
2014-07-23 10:13 ` Christian König
2014-07-23 10:52 ` Daniel Vetter
2014-07-23 12:36 ` Christian König
2014-07-23 12:42 ` Daniel Vetter
2014-07-23 13:16 ` Maarten Lankhorst
2014-07-23 14:05 ` Maarten Lankhorst
2014-07-24 13:47 ` Christian König
2014-07-23 8:01 ` Daniel Vetter
2014-07-23 8:31 ` Christian König
2014-07-23 12:35 ` Rob Clark
2014-07-22 14:05 ` Maarten Lankhorst
2014-07-22 14:24 ` Christian König
2014-07-22 14:27 ` Maarten Lankhorst
2014-07-22 14:39 ` Christian König
2014-07-22 14:47 ` Maarten Lankhorst
2014-07-22 15:16 ` Christian König
2014-07-22 15:19 ` Daniel Vetter
2014-07-22 15:42 ` Alex Deucher
2014-07-22 15:48 ` Daniel Vetter
2014-07-22 19:14 ` Jesse Barnes
2014-07-23 9:47 ` [Nouveau] " Daniel Vetter
2014-07-23 15:37 ` Jesse Barnes
2014-07-22 11:51 ` Maarten Lankhorst
2014-07-09 12:29 ` [PATCH 10/17] drm/qxl: rework to new fence interface Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 11/17] drm/vmwgfx: get rid of different types of fence_flags entirely Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 12/17] drm/vmwgfx: rework to new fence interface Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 13/17] drm/ttm: flip the switch, and convert to dma_fence Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 14/17] drm/nouveau: use rcu in nouveau_gem_ioctl_cpu_prep Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 15/17] drm/radeon: use rcu waits in some ioctls Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 16/17] drm/vmwgfx: use rcu in vmw_user_dmabuf_synccpu_grab Maarten Lankhorst
2014-07-09 12:30 ` [PATCH 17/17] drm/ttm: use rcu in core ttm Maarten Lankhorst
[not found] ` <CAHbf0-HaFi0px7QGfBErKenH7wDU08B5mxo_QhFJdDPC4WBDrQ@mail.gmail.com>
2014-07-09 13:21 ` [PATCH 00/17] Convert TTM to the new fence interface Maarten Lankhorst
2014-07-10 21:37 ` Thomas Hellström
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