[PATCH 02/11] dma-buf: add new dma_fence_chain container v2
Christian König
ckoenig.leichtzumerken at gmail.com
Mon Dec 3 11:00:28 UTC 2018
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.
>
>> + 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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