Messages in this thread | | | Subject | Re: [RFC 1/8] dma-buf/fence: add fence_collection fences | From | Christian König <> | Date | Fri, 15 Apr 2016 11:03:29 +0200 |
| |
Am 15.04.2016 um 10:02 schrieb Daniel Vetter: > On Thu, Apr 14, 2016 at 06:29:34PM -0700, Gustavo Padovan wrote: >> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk> >> >> struct fence_collection inherits from struct fence and carries a >> collection of fences that needs to be waited together. >> >> It is useful to translate a sync_file to a fence to remove the complexity >> of dealing with sync_files from DRM drivers. So even if there are many >> fences in the sync_file that needs to waited for a commit to happen >> drivers would only worry about a standard struct fence.That means that no >> changes needed to any driver besides supporting fences. >> >> fence_collection's fence doesn't belong to any timeline context. >> >> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk> >> --- >> drivers/dma-buf/Makefile | 2 +- >> drivers/dma-buf/fence-collection.c | 138 +++++++++++++++++++++++++++++++++++++ >> drivers/dma-buf/fence.c | 2 +- >> include/linux/fence-collection.h | 56 +++++++++++++++ >> include/linux/fence.h | 2 + >> 5 files changed, 198 insertions(+), 2 deletions(-) >> create mode 100644 drivers/dma-buf/fence-collection.c >> create mode 100644 include/linux/fence-collection.h >> >> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile >> index 43325a1..30b8464 100644 >> --- a/drivers/dma-buf/Makefile >> +++ b/drivers/dma-buf/Makefile >> @@ -1,3 +1,3 @@ >> -obj-y := dma-buf.o fence.o reservation.o seqno-fence.o >> +obj-y := dma-buf.o fence.o reservation.o seqno-fence.o fence-collection.o >> obj-$(CONFIG_SYNC_FILE) += sync_file.o sync_timeline.o sync_debug.o >> obj-$(CONFIG_SW_SYNC) += sw_sync.o >> diff --git a/drivers/dma-buf/fence-collection.c b/drivers/dma-buf/fence-collection.c >> new file mode 100644 >> index 0000000..8a4ecb0 >> --- /dev/null >> +++ b/drivers/dma-buf/fence-collection.c >> @@ -0,0 +1,138 @@ >> +/* >> + * fence-collection: aggregate fences to be waited together >> + * >> + * Copyright (C) 2016 Collabora Ltd >> + * Authors: >> + * Gustavo Padovan <gustavo@padovan.org> >> + * >> + * This program is free software; you can redistribute it and/or modify it >> + * under the terms of the GNU General Public License version 2 as published by >> + * the Free Software Foundation. >> + * >> + * This program is distributed in the hope that it will be useful, but WITHOUT >> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or >> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for >> + * more details. >> + */ >> + >> +#include <linux/export.h> >> +#include <linux/slab.h> >> +#include <linux/fence-collection.h> >> + >> +static const char *fence_collection_get_driver_name(struct fence *fence) >> +{ >> + struct fence_collection *collection = to_fence_collection(fence); >> + struct fence *f = collection->fences[0].fence; >> + >> + return f->ops->get_driver_name(fence); >> +}
I would rather return some constant name here instead of relying that the collection already has a fence added and that all fences are from the same driver.
>> + >> +static const char *fence_collection_get_timeline_name(struct fence *fence) >> +{ >> + return "no context"; >> +} >> + >> +static bool fence_collection_enable_signaling(struct fence *fence) >> +{ >> + struct fence_collection *collection = to_fence_collection(fence); >> + >> + return atomic_read(&collection->num_pending_fences); >> +} >> + >> +static bool fence_collection_signaled(struct fence *fence) >> +{ >> + struct fence_collection *collection = to_fence_collection(fence); >> + >> + return (atomic_read(&collection->num_pending_fences) == 0); >> +} >> + >> +static void fence_collection_release(struct fence *fence) >> +{ >> + struct fence_collection *collection = to_fence_collection(fence); >> + int i; >> + >> + for (i = 0 ; i < collection->num_fences ; i++) { >> + fence_remove_callback(collection->fences[i].fence, >> + &collection->fences[i].cb); >> + fence_put(collection->fences[i].fence); >> + } >> + >> + fence_free(fence); >> +} >> + >> +static signed long fence_collection_wait(struct fence *fence, bool intr, >> + signed long timeout) >> +{ >> + struct fence_collection *collection = to_fence_collection(fence); >> + int i; >> + >> + for (i = 0 ; i < collection->num_fences ; i++) { >> + timeout = fence_wait(collection->fences[i].fence, intr); >> + if (timeout < 0) >> + return timeout; >> + } >> + >> + return timeout; >> +} >> + >> +static const struct fence_ops fence_collection_ops = { >> + .get_driver_name = fence_collection_get_driver_name, >> + .get_timeline_name = fence_collection_get_timeline_name, >> + .enable_signaling = fence_collection_enable_signaling, >> + .signaled = fence_collection_signaled, >> + .wait = fence_collection_wait, >> + .release = fence_collection_release, >> +}; >> + >> +static void collection_check_cb_func(struct fence *fence, struct fence_cb *cb) >> +{ >> + struct fence_collection_cb *f_cb; >> + struct fence_collection *collection; >> + >> + f_cb = container_of(cb, struct fence_collection_cb, cb); >> + collection = f_cb->collection; >> + >> + if (atomic_dec_and_test(&collection->num_pending_fences)) >> + fence_signal(&collection->base); >> +} >> + >> +void fence_collection_add(struct fence_collection *collection, >> + struct fence *fence) >> +{ >> + int n = collection->num_fences; >> + >> + collection->fences[n].collection = collection; >> + collection->fences[n].fence = fence; >> + >> + if (fence_add_callback(fence, &collection->fences[n].cb, >> + collection_check_cb_func)) >> + return; >> + >> + fence_get(fence); >> + >> + collection->num_fences++; >> + atomic_inc(&collection->num_pending_fences); >> +} > For the interface I think we should not split it into _init and _add - it > shouldn't be allowed to change a collection once it's created. So probably > cleaner if we add an array of fence pointers to _init.
Amdgpu also has an implementation for a fence collection which uses a a hashtable to keep the fences grouped by context (e.g. only the latest fence is keept for each context). See amdgpu_sync.c for reference.
We should either make the collection similar in a way that you can add as many fences as you want (like the amdgpu implementation) or make it static and only add a fixed number of fences right from the beginning.
I can certainly see use cases for both, but if you want to stick with a static approach you should probably call the new object fence_array instead of fence_collection and do as Daniel suggested.
> Other nitpick: Adding the callback should (I think) only be done in > ->enable_signalling.
Yeah, I was about to complain on that as well.
Enabling signaling can have a huge overhead for some fence implementations. So it should only be used when needed
> > Finally: Have you looked into stitching together a few unit tests for > fence_collection? > > Fence collections also break the assumption that every fence is on a > timeline. fence_later and fence_is_later need to be adjusted. We also need > a special collection context to filter these out. This means > fence_collection isn't perfectly opaque abstraction. >> + >> +struct fence_collection *fence_collection_init(int num_fences) >> +{ >> + struct fence_collection *collection; >> + >> + collection = kzalloc(offsetof(struct fence_collection, >> + fences[num_fences]), GFP_KERNEL); >> + if (!collection) >> + return NULL; >> + >> + spin_lock_init(&collection->lock); >> + fence_init(&collection->base, &fence_collection_ops, &collection->lock, >> + FENCE_NO_CONTEXT, 0); >> + >> + return collection; >> +} >> +EXPORT_SYMBOL(fence_collection_init); >> + >> +void fence_collection_put(struct fence_collection *collection) >> +{ >> + fence_put(&collection->base); > Not sure a specialized _put function is useful, I'd leave it out. > >> +} >> +EXPORT_SYMBOL(fence_collection_put); >> diff --git a/drivers/dma-buf/fence.c b/drivers/dma-buf/fence.c >> index 7b05dbe..486e95c 100644 >> --- a/drivers/dma-buf/fence.c >> +++ b/drivers/dma-buf/fence.c >> @@ -35,7 +35,7 @@ EXPORT_TRACEPOINT_SYMBOL(fence_emit); >> * context or not. One device can have multiple separate contexts, >> * and they're used if some engine can run independently of another. >> */ >> -static atomic_t fence_context_counter = ATOMIC_INIT(0); >> +static atomic_t fence_context_counter = ATOMIC_INIT(1); >> >> /** >> * fence_context_alloc - allocate an array of fence contexts >> diff --git a/include/linux/fence-collection.h b/include/linux/fence-collection.h >> new file mode 100644 >> index 0000000..a798925 >> --- /dev/null >> +++ b/include/linux/fence-collection.h >> @@ -0,0 +1,56 @@ >> +/* >> + * fence-collection: aggregates fence to be waited together >> + * >> + * Copyright (C) 2016 Collabora Ltd >> + * Authors: >> + * Gustavo Padovan <gustavo@padovan.org> >> + * >> + * This program is free software; you can redistribute it and/or modify it >> + * under the terms of the GNU General Public License version 2 as published by >> + * the Free Software Foundation. >> + * >> + * This program is distributed in the hope that it will be useful, but WITHOUT >> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or >> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for >> + * more details. >> + */ >> + >> +#ifndef __LINUX_FENCE_COLLECTION_H >> +#define __LINUX_FENCE_COLLECTION_H >> + >> +#include <linux/fence.h> >> + >> +struct fence_collection_cb { >> + struct fence_cb cb; >> + struct fence *fence; >> + struct fence_collection *collection; >> +}; >> + >> +struct fence_collection { >> + struct fence base; >> + >> + spinlock_t lock; >> + struct fence_cb fence_cb; >> + atomic_t num_pending_fences; >> + int num_fences; >> + struct fence_collection_cb fences[]; >> +}; >> + >> +/** >> + * to_fence_collection - cast a fence to a fence_collection >> + * @fence: fence to cast to a fence_collection >> + * >> + * Returns NULL if the fence is not a fence_collection, >> + * or the fence_collection otherwise. >> + */ >> +static inline struct fence_collection * to_fence_collection(struct fence *fence) >> +{ > Kerneldoc claims it, but you don't check that the fence is indeed a > fence_collection. That's usually done by comparing the ops pointer. > >> + return container_of(fence, struct fence_collection, base); >> +} >> + >> +struct fence_collection *fence_collection_init(int num_fences); >> +void fence_collection_add(struct fence_collection *collection, >> + struct fence *fence); >> +void fence_collection_put(struct fence_collection *collection); >> + >> +#endif /* __LINUX_FENCE_COLLECTION_H */ >> diff --git a/include/linux/fence.h b/include/linux/fence.h >> index 2b17698..02170dd 100644 >> --- a/include/linux/fence.h >> +++ b/include/linux/fence.h >> @@ -30,6 +30,8 @@ >> #include <linux/printk.h> >> #include <linux/rcupdate.h> >> >> +#define FENCE_NO_CONTEXT 0
Might be that how amdgpu uses the fence context and sequence number is a bit questionable, but this will completely break it.
So we need a fix for amdgpu as well before this can go upstream.
Regards, Christian.
>> + >> struct fence; >> struct fence_ops; >> struct fence_cb; >> -- >> 2.5.5 >>
| |