From: Jason Gunthorpe <jgg@mellanox.com>
To: "Christian König" <christian.koenig@amd.com>
Cc: "Daniel Vetter" <daniel@ffwll.ch>,
"DRI Development" <dri-devel@lists.freedesktop.org>,
"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
linux-rdma@vger.kernel.org,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Felix Kuehling" <Felix.Kuehling@amd.com>,
"kernel test robot" <lkp@intel.com>,
"Thomas Hellström" <thomas.hellstrom@intel.com>,
"Mika Kuoppala" <mika.kuoppala@intel.com>,
linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
amd-gfx@lists.freedesktop.org,
"Chris Wilson" <chris@chris-wilson.co.uk>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 02/25] dma-fence: prime lockdep annotations
Date: Fri, 10 Jul 2020 10:48:26 -0300 [thread overview]
Message-ID: <20200710134826.GD23821@mellanox.com> (raw)
In-Reply-To: <4f4a2cf7-f505-8494-1461-bd467870481e@amd.com>
On Fri, Jul 10, 2020 at 03:01:10PM +0200, Christian König wrote:
> Am 10.07.20 um 14:54 schrieb Jason Gunthorpe:
> > On Fri, Jul 10, 2020 at 02:48:16PM +0200, Christian König wrote:
> > > Am 10.07.20 um 14:43 schrieb Jason Gunthorpe:
> > > > On Thu, Jul 09, 2020 at 10:09:11AM +0200, Daniel Vetter wrote:
> > > > > Hi Jason,
> > > > >
> > > > > Below the paragraph I've added after our discussions around dma-fences
> > > > > outside of drivers/gpu. Good enough for an ack on this, or want something
> > > > > changed?
> > > > >
> > > > > Thanks, Daniel
> > > > >
> > > > > > + * Note that only GPU drivers have a reasonable excuse for both requiring
> > > > > > + * &mmu_interval_notifier and &shrinker callbacks at the same time as having to
> > > > > > + * track asynchronous compute work using &dma_fence. No driver outside of
> > > > > > + * drivers/gpu should ever call dma_fence_wait() in such contexts.
> > > > I was hoping we'd get to 'no driver outside GPU should even use
> > > > dma_fence()'
> > > My last status was that V4L could come use dma_fences as well.
> > I'm sure lots of places *could* use it, but I think I understood that
> > it is a bad idea unless you have to fit into the DRM uAPI?
>
> It would be a bit questionable if you use the container objects we came up
> with in the DRM subsystem outside of it.
>
> But using the dma_fence itself makes sense for everything which could do
> async DMA in general.
dma_fence only possibly makes some sense if you intend to expose the
completion outside a single driver.
The prefered kernel design pattern for this is to connect things with
a function callback.
So the actual use case of dma_fence is quite narrow and tightly linked
to DRM.
I don't think we should spread this beyond DRM, I can't see a reason.
> > You are better to do something contained in the single driver where
> > locking can be analyzed.
> >
> > > I'm not 100% sure, but wouldn't MMU notifier + dma_fence be a valid use case
> > > for things like custom FPGA interfaces as well?
> > I don't think we should expand the list of drivers that use this
> > technique.
> > Drivers that can't suspend should pin memory, not use blocked
> > notifiers to created pinned memory.
>
> Agreed totally, it's a complete pain to maintain even for the GPU drivers.
>
> Unfortunately that doesn't change users from requesting it. So I'm pretty
> sure we are going to see more of this.
Kernel maintainers need to say no.
The proper way to do DMA on no-faulting hardware is page pinning.
Trying to improve performance of limited HW by using sketchy
techniques at the cost of general system stability should be a NAK.
Jason
next prev parent reply other threads:[~2020-07-10 13:48 UTC|newest]
Thread overview: 119+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 20:12 [PATCH 00/25] dma-fence annotations, round 3 Daniel Vetter
2020-07-07 20:12 ` [PATCH 01/25] dma-fence: basic lockdep annotations Daniel Vetter
2020-07-08 14:57 ` Christian König
2020-07-08 15:12 ` Daniel Vetter
2020-07-08 15:19 ` Alex Deucher
2020-07-08 15:37 ` Daniel Vetter
2020-07-14 11:09 ` Daniel Vetter
2020-07-09 7:32 ` [Intel-gfx] " Daniel Stone
2020-07-09 7:52 ` Daniel Vetter
2020-07-13 16:26 ` Daniel Vetter
2020-07-13 16:39 ` Christian König
2020-07-13 20:31 ` Dave Airlie
2020-07-07 20:12 ` [PATCH 02/25] dma-fence: prime " Daniel Vetter
2020-07-09 8:09 ` Daniel Vetter
2020-07-10 12:43 ` Jason Gunthorpe
2020-07-10 12:48 ` Christian König
2020-07-10 12:54 ` Jason Gunthorpe
2020-07-10 13:01 ` Christian König
2020-07-10 13:48 ` Jason Gunthorpe [this message]
2020-07-10 14:02 ` Daniel Vetter
2020-07-10 14:23 ` Jason Gunthorpe
2020-07-10 20:02 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 03/25] dma-buf.rst: Document why idenfinite fences are a bad idea Daniel Vetter
2020-07-09 7:36 ` [Intel-gfx] " Daniel Stone
2020-07-09 8:04 ` Daniel Vetter
2020-07-09 12:11 ` Daniel Stone
2020-07-09 12:31 ` Daniel Vetter
2020-07-09 14:28 ` Christian König
2020-07-09 11:53 ` Christian König
2020-07-09 12:33 ` [PATCH 1/2] dma-buf.rst: Document why indefinite " Daniel Vetter
2020-07-09 12:33 ` [PATCH 2/2] drm/virtio: Remove open-coded commit-tail function Daniel Vetter
2020-07-09 12:48 ` Gerd Hoffmann
2020-07-09 14:05 ` Sam Ravnborg
2020-07-14 9:13 ` Daniel Vetter
2020-08-19 12:43 ` Jiri Slaby
2020-08-19 12:47 ` Jiri Slaby
2020-08-19 13:24 ` Gerd Hoffmann
2020-08-20 6:32 ` Jiri Slaby
2020-08-21 7:01 ` Gerd Hoffmann
2020-07-10 12:30 ` [PATCH 1/2] dma-buf.rst: Document why indefinite fences are a bad idea Maarten Lankhorst
2020-07-14 17:46 ` Jason Ekstrand
2020-07-20 11:15 ` [Linaro-mm-sig] " Thomas Hellström (Intel)
2020-07-21 7:41 ` Daniel Vetter
2020-07-21 7:45 ` Christian König
2020-07-21 8:47 ` Thomas Hellström (Intel)
2020-07-21 8:55 ` Christian König
2020-07-21 9:16 ` Daniel Vetter
2020-07-21 9:24 ` Daniel Vetter
2020-07-21 9:37 ` Thomas Hellström (Intel)
2020-07-21 9:50 ` Daniel Vetter
2020-07-21 10:47 ` Thomas Hellström (Intel)
2020-07-21 13:59 ` Christian König
2020-07-21 17:46 ` Thomas Hellström (Intel)
2020-07-21 18:18 ` Daniel Vetter
2020-07-21 21:42 ` Dave Airlie
2020-07-21 22:45 ` Dave Airlie
2020-07-22 6:45 ` Thomas Hellström (Intel)
2020-07-22 7:11 ` Daniel Vetter
2020-07-22 8:05 ` Thomas Hellström (Intel)
2020-07-22 9:45 ` Daniel Vetter
2020-07-22 10:31 ` Thomas Hellström (Intel)
2020-07-22 11:39 ` Daniel Vetter
2020-07-22 12:22 ` Thomas Hellström (Intel)
2020-07-22 12:41 ` Daniel Vetter
2020-07-22 13:12 ` Thomas Hellström (Intel)
2020-07-22 14:07 ` Daniel Vetter
2020-07-22 14:23 ` Christian König
2020-07-22 14:30 ` Thomas Hellström (Intel)
2020-07-22 14:35 ` Christian König
2020-07-07 20:12 ` [PATCH 04/25] drm/vkms: Annotate vblank timer Daniel Vetter
2020-07-12 22:27 ` Rodrigo Siqueira
2020-07-14 9:57 ` Melissa Wen
2020-07-14 9:59 ` Daniel Vetter
2020-07-14 14:55 ` Melissa Wen
2020-07-14 15:23 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 05/25] drm/vblank: Annotate with dma-fence signalling section Daniel Vetter
2020-07-07 20:12 ` [PATCH 06/25] drm/amdgpu: add dma-fence annotations to atomic commit path Daniel Vetter
2020-07-07 20:12 ` [PATCH 07/25] drm/komdea: Annotate dma-fence critical section in " Daniel Vetter
2020-07-08 5:17 ` james qian wang (Arm Technology China)
2020-07-14 8:34 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 08/25] drm/malidp: " Daniel Vetter
2020-07-15 12:53 ` Liviu Dudau
2020-07-15 13:51 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 09/25] drm/atmel: Use drm_atomic_helper_commit Daniel Vetter
2020-07-07 20:37 ` Sam Ravnborg
2020-07-07 21:31 ` [PATCH] " Daniel Vetter
2020-07-14 9:55 ` Sam Ravnborg
2020-07-07 20:12 ` [PATCH 10/25] drm/imx: Annotate dma-fence critical section in commit path Daniel Vetter
2020-07-07 20:12 ` [PATCH 11/25] drm/omapdrm: " Daniel Vetter
2020-07-07 20:12 ` [PATCH 12/25] drm/rcar-du: " Daniel Vetter
2020-07-07 23:32 ` Laurent Pinchart
2020-07-14 8:39 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 13/25] drm/tegra: " Daniel Vetter
2020-07-07 20:12 ` [PATCH 14/25] drm/tidss: " Daniel Vetter
2020-07-08 9:01 ` Jyri Sarha
2020-07-07 20:12 ` [PATCH 15/25] drm/tilcdc: Use standard drm_atomic_helper_commit Daniel Vetter
2020-07-08 9:17 ` Jyri Sarha
2020-07-08 9:27 ` Daniel Vetter
2020-07-08 9:44 ` [PATCH] " Daniel Vetter
2020-07-08 10:21 ` Jyri Sarha
2020-07-08 14:20 ` Daniel Vetter
2020-07-10 11:16 ` Jyri Sarha
2020-07-14 8:32 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 16/25] drm/atomic-helper: Add dma-fence annotations Daniel Vetter
2020-07-07 20:12 ` [PATCH 17/25] drm/scheduler: use dma-fence annotations in main thread Daniel Vetter
2020-07-07 20:12 ` [PATCH 18/25] drm/amdgpu: use dma-fence annotations in cs_submit() Daniel Vetter
2020-07-07 20:12 ` [PATCH 19/25] drm/amdgpu: s/GFP_KERNEL/GFP_ATOMIC in scheduler code Daniel Vetter
2020-07-14 10:49 ` Daniel Vetter
2020-07-14 11:40 ` Christian König
2020-07-14 14:31 ` Daniel Vetter
2020-07-15 9:17 ` Christian König
2020-07-15 11:53 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 20/25] drm/amdgpu: DC also loves to allocate stuff where it shouldn't Daniel Vetter
2020-07-14 11:12 ` Daniel Vetter
2020-07-07 20:12 ` [PATCH 21/25] drm/amdgpu/dc: Stop dma_resv_lock inversion in commit_tail Daniel Vetter
2020-07-07 20:12 ` [PATCH 22/25] drm/scheduler: use dma-fence annotations in tdr work Daniel Vetter
2020-07-07 20:12 ` [PATCH 23/25] drm/amdgpu: use dma-fence annotations for gpu reset code Daniel Vetter
2020-07-07 20:12 ` [PATCH 24/25] Revert "drm/amdgpu: add fbdev suspend/resume on gpu reset" Daniel Vetter
2020-07-07 20:12 ` [PATCH 25/25] drm/amdgpu: gpu recovery does full modesets Daniel Vetter
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