From: "Christian König" <deathsimple@vodafone.de> To: "Daniel Vetter" <daniel.vetter@ffwll.ch>, "Christian König" <christian.koenig@amd.com> Cc: Dave Airlie <airlied@gmail.com>, Maarten Lankhorst <maarten.lankhorst@canonical.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 17:59:19 +0200 [thread overview] Message-ID: <53CE8A57.2000803@vodafone.de> (raw) In-Reply-To: <CAKMK7uFa8vMBV9_JenbFGnFXtV_r9dk=WjbMkkCDWcauhrDdJg@mail.gmail.com> Am 22.07.2014 17:42, schrieb Daniel Vetter: > On Tue, Jul 22, 2014 at 5:35 PM, Christian König > <christian.koenig@amd.com> wrote: >> Drivers exporting fences need to provide a fence->signaled and a fence->wait >> function, everything else like fence->enable_signaling or calling >> fence_signaled() from the driver is optional. >> >> Drivers wanting to use exported fences don't call fence->signaled or >> fence->wait in atomic or interrupt context, and not with holding any global >> locking primitives (like mmap_sem etc...). Holding locking primitives local >> to the driver is ok, as long as they don't conflict with anything possible >> used by their own fence implementation. > Well that's almost what we have right now with the exception that > drivers are allowed (actually must for correctness when updating > fences) the ww_mutexes for dma-bufs (or other buffer objects). In this case sorry for so much noise. I really haven't looked in so much detail into anything but Maarten's Radeon patches. But how does that then work right now? My impression was that it's mandatory for drivers to call fence_signaled()? > Locking > correctness is enforced with some extremely nasty lockdep annotations > + additional debugging infrastructure enabled with > CONFIG_DEBUG_WW_MUTEX_SLOWPATH. We really need to be able to hold > dma-buf ww_mutexes while updating fences or waiting for them. And > obviously for ->wait we need non-atomic context, not just > non-interrupt. Sounds mostly reasonable, but for holding the dma-buf ww_mutex, wouldn't be an RCU be more appropriate here? E.g. aren't we just interested that the current assigned fence at some point is signaled? Something like grab ww_mutexes, grab a reference to the current fence object, release ww_mutex, wait for fence, release reference to the fence object. > Agreed that any shared locks are out of the way (especially stuff like > dev->struct_mutex or other non-strictly driver-private stuff, i915 is > really bad here still). Yeah that's also an point I've wanted to note on Maartens patch. Radeon grabs the read side of it's exclusive semaphore while waiting for fences (because it assumes that the fence it waits for is a Radeon fence). Assuming that we need to wait in both directions with Prime (e.g. Intel driver needs to wait for Radeon to finish rendering and Radeon needs to wait for Intel to finish displaying), this might become a perfect example of locking inversion. > So from the core fence framework I think we already have exactly this, > and we only need to adjust the radeon implementation a bit to make it > less risky and invasive to the radeon driver logic. Agree. Well the biggest problem I see is that exclusive semaphore I need to take when anything calls into the driver. For the fence code I need to move that down into the fence->signaled handler, cause that now can be called from outside the driver. Maarten solved this by telling the driver in the lockup handler (where we grab the write side of the exclusive lock) that all interrupts are already enabled, so that fence->signaled hopefully wouldn't mess with the hardware at all. While this probably works, it just leaves me with a feeling that we are doing something wrong here. Christian. > -Daniel
WARNING: multiple messages have this Message-ID (diff)
From: "Christian König" <deathsimple@vodafone.de> To: "Daniel Vetter" <daniel.vetter@ffwll.ch>, "Christian König" <christian.koenig@amd.com> Cc: Thomas Hellstrom <thellstrom@vmware.com>, nouveau <nouveau@lists.freedesktop.org>, LKML <linux-kernel@vger.kernel.org>, dri-devel <dri-devel@lists.freedesktop.org>, "Deucher, Alexander" <alexander.deucher@amd.com>, Ben Skeggs <bskeggs@redhat.com> Subject: Re: [Nouveau] [PATCH 09/17] drm/radeon: use common fence implementation for fences Date: Tue, 22 Jul 2014 17:59:19 +0200 [thread overview] Message-ID: <53CE8A57.2000803@vodafone.de> (raw) In-Reply-To: <CAKMK7uFa8vMBV9_JenbFGnFXtV_r9dk=WjbMkkCDWcauhrDdJg@mail.gmail.com> Am 22.07.2014 17:42, schrieb Daniel Vetter: > On Tue, Jul 22, 2014 at 5:35 PM, Christian König > <christian.koenig@amd.com> wrote: >> Drivers exporting fences need to provide a fence->signaled and a fence->wait >> function, everything else like fence->enable_signaling or calling >> fence_signaled() from the driver is optional. >> >> Drivers wanting to use exported fences don't call fence->signaled or >> fence->wait in atomic or interrupt context, and not with holding any global >> locking primitives (like mmap_sem etc...). Holding locking primitives local >> to the driver is ok, as long as they don't conflict with anything possible >> used by their own fence implementation. > Well that's almost what we have right now with the exception that > drivers are allowed (actually must for correctness when updating > fences) the ww_mutexes for dma-bufs (or other buffer objects). In this case sorry for so much noise. I really haven't looked in so much detail into anything but Maarten's Radeon patches. But how does that then work right now? My impression was that it's mandatory for drivers to call fence_signaled()? > Locking > correctness is enforced with some extremely nasty lockdep annotations > + additional debugging infrastructure enabled with > CONFIG_DEBUG_WW_MUTEX_SLOWPATH. We really need to be able to hold > dma-buf ww_mutexes while updating fences or waiting for them. And > obviously for ->wait we need non-atomic context, not just > non-interrupt. Sounds mostly reasonable, but for holding the dma-buf ww_mutex, wouldn't be an RCU be more appropriate here? E.g. aren't we just interested that the current assigned fence at some point is signaled? Something like grab ww_mutexes, grab a reference to the current fence object, release ww_mutex, wait for fence, release reference to the fence object. > Agreed that any shared locks are out of the way (especially stuff like > dev->struct_mutex or other non-strictly driver-private stuff, i915 is > really bad here still). Yeah that's also an point I've wanted to note on Maartens patch. Radeon grabs the read side of it's exclusive semaphore while waiting for fences (because it assumes that the fence it waits for is a Radeon fence). Assuming that we need to wait in both directions with Prime (e.g. Intel driver needs to wait for Radeon to finish rendering and Radeon needs to wait for Intel to finish displaying), this might become a perfect example of locking inversion. > So from the core fence framework I think we already have exactly this, > and we only need to adjust the radeon implementation a bit to make it > less risky and invasive to the radeon driver logic. Agree. Well the biggest problem I see is that exclusive semaphore I need to take when anything calls into the driver. For the fence code I need to move that down into the fence->signaled handler, cause that now can be called from outside the driver. Maarten solved this by telling the driver in the lockup handler (where we grab the write side of the exclusive lock) that all interrupts are already enabled, so that fence->signaled hopefully wouldn't mess with the hardware at all. While this probably works, it just leaves me with a feeling that we are doing something wrong here. Christian. > -Daniel _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2014-07-22 15:59 UTC|newest] Thread overview: 165+ 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 ` 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 12:57 ` Deucher, Alexander 2014-07-09 13:23 ` [PATCH v2 " Maarten Lankhorst 2014-07-09 13:23 ` Maarten Lankhorst 2014-07-10 17:27 ` Alex Deucher 2014-07-10 17:27 ` Alex Deucher 2014-07-22 4:05 ` [PATCH " Dave Airlie 2014-07-22 4:05 ` Dave Airlie 2014-07-22 4:05 ` Dave Airlie 2014-07-22 8:43 ` Christian König 2014-07-22 8:43 ` Christian König 2014-07-22 11:46 ` Daniel Vetter 2014-07-22 11:46 ` Daniel Vetter 2014-07-22 11:52 ` Daniel Vetter 2014-07-22 11:52 ` Daniel Vetter 2014-07-22 11:57 ` Daniel Vetter 2014-07-22 11:57 ` Daniel Vetter 2014-07-22 12:19 ` Christian König 2014-07-22 12:19 ` Christian König 2014-07-22 13:26 ` [Nouveau] " Daniel Vetter 2014-07-22 13:26 ` Daniel Vetter 2014-07-22 13:45 ` Christian König 2014-07-22 13:45 ` Christian König 2014-07-22 14:44 ` [Nouveau] " Maarten Lankhorst 2014-07-22 14:44 ` Maarten Lankhorst 2014-07-22 15:02 ` [Nouveau] " Christian König 2014-07-22 15:18 ` Maarten Lankhorst 2014-07-22 15:17 ` Daniel Vetter 2014-07-22 15:17 ` Daniel Vetter 2014-07-22 15:35 ` [Nouveau] " Christian König 2014-07-22 15:35 ` Christian König 2014-07-22 15:42 ` Daniel Vetter 2014-07-22 15:42 ` Daniel Vetter 2014-07-22 15:59 ` Christian König [this message] 2014-07-22 15:59 ` Christian König 2014-07-22 16:21 ` Daniel Vetter 2014-07-22 16:21 ` Daniel Vetter 2014-07-22 16:39 ` Christian König 2014-07-22 16:39 ` Christian König 2014-07-22 16:52 ` Daniel Vetter 2014-07-22 16:52 ` Daniel Vetter 2014-07-22 16:43 ` Daniel Vetter 2014-07-22 16:43 ` Daniel Vetter 2014-07-23 6:40 ` Maarten Lankhorst 2014-07-23 6:40 ` Maarten Lankhorst 2014-07-23 6:52 ` Christian König 2014-07-23 6:52 ` Christian König 2014-07-23 7:02 ` [Nouveau] " Daniel Vetter 2014-07-23 7:02 ` Daniel Vetter 2014-07-23 7:06 ` [Nouveau] " Maarten Lankhorst 2014-07-23 7:06 ` Maarten Lankhorst 2014-07-23 7:09 ` Daniel Vetter 2014-07-23 7:09 ` Daniel Vetter 2014-07-23 7:15 ` Christian König 2014-07-23 7:15 ` Christian König 2014-07-23 7:32 ` [Nouveau] " Maarten Lankhorst 2014-07-23 7:32 ` Maarten Lankhorst 2014-07-23 7:41 ` Christian König 2014-07-23 7:41 ` Christian König 2014-07-23 7:26 ` [Nouveau] " Christian König 2014-07-23 7:26 ` Christian König 2014-07-23 7:31 ` Daniel Vetter 2014-07-23 7:31 ` Daniel Vetter 2014-07-23 7:37 ` Christian König 2014-07-23 7:37 ` Christian König 2014-07-23 7:51 ` [Nouveau] " Maarten Lankhorst 2014-07-23 7:51 ` Maarten Lankhorst 2014-07-23 7:58 ` [Nouveau] " Christian König 2014-07-23 7:58 ` Christian König 2014-07-23 8:07 ` [Nouveau] " Daniel Vetter 2014-07-23 8:07 ` Daniel Vetter 2014-07-23 8:20 ` [Nouveau] " Christian König 2014-07-23 8:20 ` Christian König 2014-07-23 8:25 ` Maarten Lankhorst 2014-07-23 8:25 ` Maarten Lankhorst 2014-07-23 8:42 ` [Nouveau] " Daniel Vetter 2014-07-23 8:42 ` Daniel Vetter 2014-07-23 8:46 ` Christian König 2014-07-23 8:46 ` Christian König 2014-07-23 8:54 ` [Nouveau] " Daniel Vetter 2014-07-23 8:54 ` Daniel Vetter 2014-07-23 9:27 ` [Nouveau] " Christian König 2014-07-23 9:27 ` Christian König 2014-07-23 9:30 ` [Nouveau] " Daniel Vetter 2014-07-23 9:30 ` Daniel Vetter 2014-07-23 9:36 ` [Nouveau] " Christian König 2014-07-23 9:36 ` Christian König 2014-07-23 9:38 ` [Nouveau] " Maarten Lankhorst 2014-07-23 9:38 ` Maarten Lankhorst 2014-07-23 9:39 ` Christian König 2014-07-23 9:39 ` Christian König 2014-07-23 9:39 ` [Nouveau] " Daniel Vetter 2014-07-23 9:39 ` Daniel Vetter 2014-07-23 9:44 ` Daniel Vetter 2014-07-23 9:44 ` Daniel Vetter 2014-07-23 9:47 ` [Nouveau] " Christian König 2014-07-23 9:47 ` Christian König 2014-07-23 9:52 ` Daniel Vetter 2014-07-23 9:52 ` Daniel Vetter 2014-07-23 9:55 ` [Nouveau] " Maarten Lankhorst 2014-07-23 9:55 ` Maarten Lankhorst 2014-07-23 10:13 ` [Nouveau] " Christian König 2014-07-23 10:13 ` Christian König 2014-07-23 10:52 ` [Nouveau] " Daniel Vetter 2014-07-23 10:52 ` Daniel Vetter 2014-07-23 12:36 ` Christian König 2014-07-23 12:36 ` Christian König 2014-07-23 12:42 ` Daniel Vetter 2014-07-23 12:42 ` Daniel Vetter 2014-07-23 13:16 ` Maarten Lankhorst 2014-07-23 13:16 ` Maarten Lankhorst 2014-07-23 14:05 ` [Nouveau] " Maarten Lankhorst 2014-07-23 14:05 ` Maarten Lankhorst 2014-07-24 13:47 ` [Nouveau] " Christian König 2014-07-24 13:47 ` Christian König 2014-07-23 8:01 ` Daniel Vetter 2014-07-23 8:01 ` Daniel Vetter 2014-07-23 8:31 ` Christian König 2014-07-23 8:31 ` Christian König 2014-07-23 12:35 ` Rob Clark 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 15:19 ` Daniel Vetter 2014-07-22 15:42 ` Alex Deucher 2014-07-22 15:42 ` Alex Deucher 2014-07-22 15:48 ` Daniel Vetter 2014-07-22 15:48 ` Daniel Vetter 2014-07-22 19:14 ` Jesse Barnes 2014-07-22 19:14 ` Jesse Barnes 2014-07-23 9:47 ` [Nouveau] " Daniel Vetter 2014-07-23 9:47 ` Daniel Vetter 2014-07-23 15:37 ` [Nouveau] " Jesse Barnes 2014-07-23 15:37 ` Jesse Barnes 2014-07-22 11:51 ` Maarten Lankhorst 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 2014-07-09 13:09 ` [PATCH 00/17] Convert TTM to the new fence interface Mike Lothian 2014-07-09 13:21 ` Maarten Lankhorst 2014-07-09 13:21 ` Maarten Lankhorst 2014-07-10 21:37 ` Thomas Hellström 2014-07-10 21:37 ` Thomas Hellström
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