[PATCH 02/11] dma-buf: add new dma_fence_chain container v2
Christian König
ckoenig.leichtzumerken at gmail.com
Mon Dec 3 13:28:18 UTC 2018
Am 03.12.18 um 14:18 schrieb Chunming Zhou:
>
> 在 2018/12/3 19:00, Christian König 写道:
>> Am 03.12.18 um 06:25 schrieb zhoucm1:
>>>
>>> On 2018年11月28日 22:50, Christian König wrote:
>>>> Lockless container implementation similar to a dma_fence_array, but
>>>> with
>>>> only two elements per node and automatic garbage collection.
>>>>
>>>> v2: properly document dma_fence_chain_for_each, add
>>>> dma_fence_chain_find_seqno,
>>>> drop prev reference during garbage collection if it's not a
>>>> chain fence.
>>>>
>>>> Signed-off-by: Christian König <christian.koenig at amd.com>
>>>> ---
>>>> drivers/dma-buf/Makefile | 3 +-
>>>> drivers/dma-buf/dma-fence-chain.c | 235
>>>> ++++++++++++++++++++++++++++++++++++++
>>>> include/linux/dma-fence-chain.h | 79 +++++++++++++
>>>> 3 files changed, 316 insertions(+), 1 deletion(-)
>>>> create mode 100644 drivers/dma-buf/dma-fence-chain.c
>>>> create mode 100644 include/linux/dma-fence-chain.h
>>>>
>>>> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
>>>> index 0913a6ccab5a..1f006e083eb9 100644
>>>> --- a/drivers/dma-buf/Makefile
>>>> +++ b/drivers/dma-buf/Makefile
>>>> @@ -1,4 +1,5 @@
>>>> -obj-y := dma-buf.o dma-fence.o dma-fence-array.o reservation.o
>>>> seqno-fence.o
>>>> +obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
>>>> + reservation.o seqno-fence.o
>>>> obj-$(CONFIG_SYNC_FILE) += sync_file.o
>>>> obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
>>>> obj-$(CONFIG_UDMABUF) += udmabuf.o
>>>> diff --git a/drivers/dma-buf/dma-fence-chain.c
>>>> b/drivers/dma-buf/dma-fence-chain.c
>>>> new file mode 100644
>>>> index 000000000000..de05101fc48d
>>>> --- /dev/null
>>>> +++ b/drivers/dma-buf/dma-fence-chain.c
>>>> @@ -0,0 +1,235 @@
>>>> +/*
>>>> + * fence-chain: chain fences together in a timeline
>>>> + *
>>>> + * Copyright (C) 2018 Advanced Micro Devices, Inc.
>>>> + * Authors:
>>>> + * Christian König <christian.koenig at amd.com>
>>>> + *
>>>> + * 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/dma-fence-chain.h>
>>>> +
>>>> +static bool dma_fence_chain_enable_signaling(struct dma_fence *fence);
>>>> +
>>>> +/**
>>>> + * dma_fence_chain_get_prev - use RCU to get a reference to the
>>>> previous fence
>>>> + * @chain: chain node to get the previous node from
>>>> + *
>>>> + * Use dma_fence_get_rcu_safe to get a reference to the previous
>>>> fence of the
>>>> + * chain node.
>>>> + */
>>>> +static struct dma_fence *dma_fence_chain_get_prev(struct
>>>> dma_fence_chain *chain)
>>>> +{
>>>> + struct dma_fence *prev;
>>>> +
>>>> + rcu_read_lock();
>>>> + prev = dma_fence_get_rcu_safe(&chain->prev);
>>>> + rcu_read_unlock();
>>>> + return prev;
>>>> +}
>>>> +
>>>> +/**
>>>> + * dma_fence_chain_walk - chain walking function
>>>> + * @fence: current chain node
>>>> + *
>>>> + * Walk the chain to the next node. Returns the next fence or NULL
>>>> if we are at
>>>> + * the end of the chain. Garbage collects chain nodes which are
>>>> already
>>>> + * signaled.
>>>> + */
>>>> +struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence)
>>>> +{
>>>> + struct dma_fence_chain *chain, *prev_chain;
>>>> + struct dma_fence *prev, *replacement, *tmp;
>>>> +
>>>> + chain = to_dma_fence_chain(fence);
>>>> + if (!chain) {
>>>> + dma_fence_put(fence);
>>>> + return NULL;
>>>> + }
>>>> +
>>>> + while ((prev = dma_fence_chain_get_prev(chain))) {
>>>> +
>>>> + prev_chain = to_dma_fence_chain(prev);
>>>> + if (prev_chain) {
>>>> + if (!dma_fence_is_signaled(prev_chain->fence))
>>>> + break;
>>>> +
>>>> + replacement = dma_fence_chain_get_prev(prev_chain);
>>>> + } else {
>>>> + if (!dma_fence_is_signaled(prev))
>>>> + break;
>>>> +
>>>> + replacement = NULL;
>>>> + }
>>>> +
>>>> + tmp = cmpxchg(&chain->prev, prev, replacement);
>>>> + if (tmp == prev)
>>>> + dma_fence_put(tmp);
>>>> + else
>>>> + dma_fence_put(replacement);
>>>> + dma_fence_put(prev);
>>>> + }
>>>> +
>>>> + dma_fence_put(fence);
>>>> + return prev;
>>>> +}
>>>> +EXPORT_SYMBOL(dma_fence_chain_walk);
>>>> +
>>>> +/**
>>>> + * dma_fence_chain_find_seqno - find fence chain node by seqno
>>>> + * @pfence: pointer to the chain node where to start
>>>> + * @seqno: the sequence number to search for
>>>> + *
>>>> + * Advance the fence pointer to the chain node which will signal
>>>> this sequence
>>>> + * number. If no sequence number is provided then this is a no-op.
>>>> + *
>>>> + * Returns EINVAL if the fence is not a chain node or the sequence
>>>> number has
>>>> + * not yet advanced far enough.
>>>> + */
>>>> +int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t
>>>> seqno)
>>>> +{
>>>> + struct dma_fence_chain *chain;
>>>> +
>>>> + if (!seqno)
>>>> + return 0;
>>>> +
>>>> + chain = to_dma_fence_chain(*pfence);
>>>> + if (!chain || chain->base.seqno < seqno)
>>>> + return -EINVAL;
>>>> +
>>>> + dma_fence_chain_for_each(*pfence) {
>>>> + if ((*pfence)->context != chain->base.context ||
>>>> + to_dma_fence_chain(*pfence)->prev_seqno < seqno)
>>>> + break;
>>>> + }
>>>> + dma_fence_put(&chain->base);
>>>> +
>>>> + return 0;
>>>> +}
>>>> +EXPORT_SYMBOL(dma_fence_chain_find_seqno);
>>>> +
>>>> +static const char *dma_fence_chain_get_driver_name(struct dma_fence
>>>> *fence)
>>>> +{
>>>> + return "dma_fence_chain";
>>>> +}
>>>> +
>>>> +static const char *dma_fence_chain_get_timeline_name(struct
>>>> dma_fence *fence)
>>>> +{
>>>> + return "unbound";
>>>> +}
>>>> +
>>>> +static void dma_fence_chain_irq_work(struct irq_work *work)
>>>> +{
>>>> + struct dma_fence_chain *chain;
>>>> +
>>>> + chain = container_of(work, typeof(*chain), work);
>>>> +
>>>> + /* Try to rearm the callback */
>>>> + if (!dma_fence_chain_enable_signaling(&chain->base))
>>>> + /* Ok, we are done. No more unsignaled fences left */
>>>> + dma_fence_signal(&chain->base);
>>>> +}
>>>> +
>>>> +static void dma_fence_chain_cb(struct dma_fence *f, struct
>>>> dma_fence_cb *cb)
>>>> +{
>>>> + struct dma_fence_chain *chain;
>>>> +
>>>> + chain = container_of(cb, typeof(*chain), cb);
>>>> + irq_work_queue(&chain->work);
>>>> + dma_fence_put(f);
>>>> +}
>>>> +
>>>> +static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
>>>> +{
>>>> + struct dma_fence_chain *head = to_dma_fence_chain(fence);
>>>> +
>>>> + dma_fence_chain_for_each(fence) {
>>>> + struct dma_fence_chain *chain = to_dma_fence_chain(fence);
>>>> + struct dma_fence *f = chain ? chain->fence : fence;
>>>> +
>>>> + if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb))
>>>> + return true;
>>>> + }
>>>> + return false;
>>>> +}
>>>> +
>>>> +static bool dma_fence_chain_signaled(struct dma_fence *fence)
>>>> +{
>>>> + dma_fence_chain_for_each(fence) {
>>>> + struct dma_fence_chain *chain = to_dma_fence_chain(fence);
>>>> + struct dma_fence *f = chain ? chain->fence : fence;
>>>> +
>>>> + if (!dma_fence_is_signaled(f)) {
>>>> + dma_fence_put(fence);
>>>> + return false;
>>>> + }
>>>> + }
>>>> +
>>>> + return true;
>>>> +}
>>>> +
>>>> +static void dma_fence_chain_release(struct dma_fence *fence)
>>>> +{
>>>> + struct dma_fence_chain *chain = to_dma_fence_chain(fence);
>>>> +
>>>> + dma_fence_put(chain->prev);
>>>> + dma_fence_put(chain->fence);
>>>> + dma_fence_free(fence);
>>>> +}
>>>> +
>>>> +const struct dma_fence_ops dma_fence_chain_ops = {
>>>> + .get_driver_name = dma_fence_chain_get_driver_name,
>>>> + .get_timeline_name = dma_fence_chain_get_timeline_name,
>>>> + .enable_signaling = dma_fence_chain_enable_signaling,
>>>> + .signaled = dma_fence_chain_signaled,
>>>> + .release = dma_fence_chain_release,
>>>> +};
>>>> +EXPORT_SYMBOL(dma_fence_chain_ops);
>>>> +
>>>> +/**
>>>> + * dma_fence_chain_init - initialize a fence chain
>>>> + * @chain: the chain node to initialize
>>>> + * @prev: the previous fence
>>>> + * @fence: the current fence
>>>> + *
>>>> + * Initialize a new chain node and either start a new chain or add
>>>> the node to
>>>> + * the existing chain of the previous fence.
>>>> + */
>>>> +void dma_fence_chain_init(struct dma_fence_chain *chain,
>>>> + struct dma_fence *prev,
>>>> + struct dma_fence *fence,
>>>> + uint64_t seqno)
>>>> +{
>>>> + struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
>>>> + uint64_t context;
>>>> +
>>>> + spin_lock_init(&chain->lock);
>>>> + chain->prev = prev;
>>>> + chain->fence = fence;
>>>> + chain->prev_seqno = 0;
>>>> + init_irq_work(&chain->work, dma_fence_chain_irq_work);
>>>> +
>>>> + /* Try to reuse the context of the previous chain node. */
>>>> + if (prev_chain && seqno > prev->seqno &&
>>>> + __dma_fence_is_later(seqno, prev->seqno)) {
>>> As your patch#1 makes __dma_fence_is_later only be valid for 32bit,
>>> we cannot use it for 64bit here, we should remove it from here, just
>>> compare seqno directly.
>> That is intentional. We must make sure that the number both increments
>> as 64bit number as well as not wraps around as 32bit number.
>>
>> In other words the largest difference between two sequence numbers
>> userspace is allowed to submit is 1<<31.
> Why? no one can make sure that, application users would only think it is
> an uint64 sequence nubmer, and they can signal any advanced point. I
> already see umd guys writing timeline test use max_uint64-1 as a final
> signal.
> We shouldn't add this limitation here.
We need to be backward compatible to hardware which can only do 32bit
signaling with the dma-fence implementation.
Otherwise dma_fence_later() could return an inconsistent result and
break at other places.
So if userspace wants to use more than 1<<31 difference between sequence
numbers we need to push back on this.
Christian.
>
> -David
>
>>>> + context = prev->context;
>>>> + chain->prev_seqno = prev->seqno;
>>>> + } else {
>>>> + context = dma_fence_context_alloc(1);
>>>> + /* Make sure that we always have a valid sequence number. */
>>>> + if (prev_chain)
>>>> + seqno = max(prev->seqno, seqno);
>>> I still cannot judge if this case is proper, but I prefer we just
>>> drop it when seqno is <= last seqno.
>>> we can image that when we enable export/import, we could mess them.
>>> So we shouldn't change timeline existing signal point any time.
>> Yeah, but we can't lose fences either. This is the most defensive
>> approach I can think of.
>>
>> E.g. we still ad the fence, but start a new timeline so all queries
>> for all previous sequence number will always wait for everything.
>>
>> Regards,
>> Christian.
>>
>>> -David
>>>> + }
>>>> +
>>>> + dma_fence_init(&chain->base, &dma_fence_chain_ops,
>>>> + &chain->lock, context, seqno);
>>>> +}
>>>> +EXPORT_SYMBOL(dma_fence_chain_init);
>>>> diff --git a/include/linux/dma-fence-chain.h
>>>> b/include/linux/dma-fence-chain.h
>>>> new file mode 100644
>>>> index 000000000000..3bb0efd6bc65
>>>> --- /dev/null
>>>> +++ b/include/linux/dma-fence-chain.h
>>>> @@ -0,0 +1,79 @@
>>>> +/*
>>>> + * fence-chain: chain fences together in a timeline
>>>> + *
>>>> + * Copyright (C) 2018 Advanced Micro Devices, Inc.
>>>> + * Authors:
>>>> + * Christian König <christian.koenig at amd.com>
>>>> + *
>>>> + * 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_DMA_FENCE_CHAIN_H
>>>> +#define __LINUX_DMA_FENCE_CHAIN_H
>>>> +
>>>> +#include <linux/dma-fence.h>
>>>> +#include <linux/irq_work.h>
>>>> +
>>>> +/**
>>>> + * struct dma_fence_chain - fence to represent an node of a fence
>>>> chain
>>>> + * @base: fence base class
>>>> + * @lock: spinlock for fence handling
>>>> + * @prev: previous fence of the chain
>>>> + * @prev_seqno: original previous seqno before garbage collection
>>>> + * @fence: encapsulated fence
>>>> + * @cb: callback structure for signaling
>>>> + * @work: irq work item for signaling
>>>> + */
>>>> +struct dma_fence_chain {
>>>> + struct dma_fence base;
>>>> + spinlock_t lock;
>>>> + struct dma_fence *prev;
>>>> + u64 prev_seqno;
>>>> + struct dma_fence *fence;
>>>> + struct dma_fence_cb cb;
>>>> + struct irq_work work;
>>>> +};
>>>> +
>>>> +extern const struct dma_fence_ops dma_fence_chain_ops;
>>>> +
>>>> +/**
>>>> + * to_dma_fence_chain - cast a fence to a dma_fence_chain
>>>> + * @fence: fence to cast to a dma_fence_array
>>>> + *
>>>> + * Returns NULL if the fence is not a dma_fence_chain,
>>>> + * or the dma_fence_chain otherwise.
>>>> + */
>>>> +static inline struct dma_fence_chain *
>>>> +to_dma_fence_chain(struct dma_fence *fence)
>>>> +{
>>>> + if (!fence || fence->ops != &dma_fence_chain_ops)
>>>> + return NULL;
>>>> +
>>>> + return container_of(fence, struct dma_fence_chain, base);
>>>> +}
>>>> +
>>>> +/**
>>>> + * dma_fence_chain_for_each - iterate over all fences in chain
>>>> + * @fence: starting point as well as current fence
>>>> + *
>>>> + * Iterate over all fences in the chain. We keep a reference to the
>>>> current
>>>> + * fence while inside the loop which must be dropped when breaking
>>>> out.
>>>> + */
>>>> +#define dma_fence_chain_for_each(fence) \
>>>> + for (dma_fence_get(fence);fence;fence=dma_fence_chain_walk(fence))
>>>> +
>>>> +struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence);
>>>> +int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t
>>>> seqno);
>>>> +void dma_fence_chain_init(struct dma_fence_chain *chain,
>>>> + struct dma_fence *prev,
>>>> + struct dma_fence *fence,
>>>> + uint64_t seqno);
>>>> +
>>>> +#endif /* __LINUX_DMA_FENCE_CHAIN_H */
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