Re: [PATCH v2 08/20] util/dsa: Implement DSA task enqueue and dequeue.

[Fabiano Rosas]

Hao Xiang <hao.xiang@bytedance.com> writes:

> * Use a safe thread queue for DSA task enqueue/dequeue.
> * Implement DSA task submission.
> * Implement DSA batch task submission.
>
> Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
> ---
>  include/qemu/dsa.h |  35 ++++++++
>  util/dsa.c         | 196 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 231 insertions(+)
>
> diff --git a/include/qemu/dsa.h b/include/qemu/dsa.h
> index 30246b507e..23f55185be 100644
> --- a/include/qemu/dsa.h
> +++ b/include/qemu/dsa.h
> @@ -12,6 +12,41 @@
>  #include <linux/idxd.h>
>  #include "x86intrin.h"
>  
> +enum dsa_task_type {

Our coding style requires CamelCase for enums and typedef'ed structures.

> +    DSA_TASK = 0,
> +    DSA_BATCH_TASK
> +};
> +
> +enum dsa_task_status {
> +    DSA_TASK_READY = 0,
> +    DSA_TASK_PROCESSING,
> +    DSA_TASK_COMPLETION
> +};
> +
> +typedef void (*buffer_zero_dsa_completion_fn)(void *);

We don't really need the "buffer_zero" mention in any of this
code. Simply dsa_batch_task or batch_task would suffice.

> +
> +typedef struct buffer_zero_batch_task {
> +    struct dsa_hw_desc batch_descriptor;
> +    struct dsa_hw_desc *descriptors;
> +    struct dsa_completion_record batch_completion 
> __attribute__((aligned(32)));
> +    struct dsa_completion_record *completions;
> +    struct dsa_device_group *group;
> +    struct dsa_device *device;
> +    buffer_zero_dsa_completion_fn completion_callback;
> +    QemuSemaphore sem_task_complete;
> +    enum dsa_task_type task_type;
> +    enum dsa_task_status status;
> +    bool *results;
> +    int batch_size;
> +    QSIMPLEQ_ENTRY(buffer_zero_batch_task) entry;
> +} buffer_zero_batch_task;

I see data specific to this implementation and data coming from the
library, maybe these would be better organized in two separate
structures with the qemu-specific having a pointer to the generic
one. Looking ahead in the series, there seems to be migration data
coming into this as well.

> +
> +#else
> +
> +struct buffer_zero_batch_task {
> +    bool *results;
> +};
> +
>  #endif
>  
>  /**
> diff --git a/util/dsa.c b/util/dsa.c
> index 8edaa892ec..f82282ce99 100644
> --- a/util/dsa.c
> +++ b/util/dsa.c
> @@ -245,6 +245,200 @@ dsa_device_group_get_next_device(struct 
> dsa_device_group *group)
>      return &group->dsa_devices[current];
>  }
>  
> +/**
> + * @brief Empties out the DSA task queue.
> + *
> + * @param group A pointer to the DSA device group.
> + */
> +static void
> +dsa_empty_task_queue(struct dsa_device_group *group)
> +{
> +    qemu_mutex_lock(&group->task_queue_lock);
> +    dsa_task_queue *task_queue = &group->task_queue;
> +    while (!QSIMPLEQ_EMPTY(task_queue)) {
> +        QSIMPLEQ_REMOVE_HEAD(task_queue, entry);
> +    }
> +    qemu_mutex_unlock(&group->task_queue_lock);
> +}
> +
> +/**
> + * @brief Adds a task to the DSA task queue.
> + *
> + * @param group A pointer to the DSA device group.
> + * @param context A pointer to the DSA task to enqueue.
> + *
> + * @return int Zero if successful, otherwise a proper error code.
> + */
> +static int
> +dsa_task_enqueue(struct dsa_device_group *group,
> +                 struct buffer_zero_batch_task *task)
> +{
> +    dsa_task_queue *task_queue = &group->task_queue;
> +    QemuMutex *task_queue_lock = &group->task_queue_lock;
> +    QemuCond *task_queue_cond = &group->task_queue_cond;
> +
> +    bool notify = false;
> +
> +    qemu_mutex_lock(task_queue_lock);
> +
> +    if (!group->running) {
> +        fprintf(stderr, "DSA: Tried to queue task to stopped device 
> queue\n");
> +        qemu_mutex_unlock(task_queue_lock);
> +        return -1;
> +    }
> +
> +    // The queue is empty. This enqueue operation is a 0->1 transition.
> +    if (QSIMPLEQ_EMPTY(task_queue))
> +        notify = true;
> +
> +    QSIMPLEQ_INSERT_TAIL(task_queue, task, entry);
> +
> +    // We need to notify the waiter for 0->1 transitions.
> +    if (notify)
> +        qemu_cond_signal(task_queue_cond);
> +
> +    qemu_mutex_unlock(task_queue_lock);
> +
> +    return 0;
> +}
> +
> +/**
> + * @brief Takes a DSA task out of the task queue.
> + *
> + * @param group A pointer to the DSA device group.
> + * @return buffer_zero_batch_task* The DSA task being dequeued.
> + */
> +__attribute__((unused))
> +static struct buffer_zero_batch_task *
> +dsa_task_dequeue(struct dsa_device_group *group)
> +{
> +    struct buffer_zero_batch_task *task = NULL;
> +    dsa_task_queue *task_queue = &group->task_queue;
> +    QemuMutex *task_queue_lock = &group->task_queue_lock;
> +    QemuCond *task_queue_cond = &group->task_queue_cond;
> +
> +    qemu_mutex_lock(task_queue_lock);
> +
> +    while (true) {
> +        if (!group->running)
> +            goto exit;
> +        task = QSIMPLEQ_FIRST(task_queue);
> +        if (task != NULL) {
> +            break;
> +        }
> +        qemu_cond_wait(task_queue_cond, task_queue_lock);
> +    }
> +
> +    QSIMPLEQ_REMOVE_HEAD(task_queue, entry);
> +
> +exit:
> +    qemu_mutex_unlock(task_queue_lock);
> +    return task;
> +}
> +
> +/**
> + * @brief Submits a DSA work item to the device work queue.
> + *
> + * @param wq A pointer to the DSA work queue's device memory.
> + * @param descriptor A pointer to the DSA work item descriptor.
> + *
> + * @return Zero if successful, non-zero otherwise.
> + */
> +static int
> +submit_wi_int(void *wq, struct dsa_hw_desc *descriptor)
> +{
> +    uint64_t retry = 0;
> +
> +    _mm_sfence();
> +
> +    while (true) {
> +        if (_enqcmd(wq, descriptor) == 0) {
> +            break;
> +        }
> +        retry++;
> +        if (retry > max_retry_count) {

'max_retry_count' is UINT64_MAX so 'retry' will wrap around.

> +            fprintf(stderr, "Submit work retry %lu times.\n", retry);
> +            exit(1);

Is this not the case where we'd fallback to the CPU?

You should not exit() here, but return non-zero as the documentation
mentions and the callers expect.

> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +/**
> + * @brief Synchronously submits a DSA work item to the
> + *        device work queue.
> + *
> + * @param wq A pointer to the DSA worjk queue's device memory.
> + * @param descriptor A pointer to the DSA work item descriptor.
> + *
> + * @return int Zero if successful, non-zero otherwise.
> + */
> +__attribute__((unused))
> +static int
> +submit_wi(void *wq, struct dsa_hw_desc *descriptor)
> +{
> +    return submit_wi_int(wq, descriptor);
> +}
> +
> +/**
> + * @brief Asynchronously submits a DSA work item to the
> + *        device work queue.
> + *
> + * @param task A pointer to the buffer zero task.
> + *
> + * @return int Zero if successful, non-zero otherwise.
> + */
> +__attribute__((unused))
> +static int
> +submit_wi_async(struct buffer_zero_batch_task *task)
> +{
> +    struct dsa_device_group *device_group = task->group;
> +    struct dsa_device *device_instance = task->device;
> +    int ret;
> +
> +    assert(task->task_type == DSA_TASK);
> +
> +    task->status = DSA_TASK_PROCESSING;
> +
> +    ret = submit_wi_int(device_instance->work_queue,
> +                        &task->descriptors[0]);
> +    if (ret != 0)
> +        return ret;
> +
> +    return dsa_task_enqueue(device_group, task);
> +}
> +
> +/**
> + * @brief Asynchronously submits a DSA batch work item to the
> + *        device work queue.
> + *
> + * @param batch_task A pointer to the batch buffer zero task.
> + *
> + * @return int Zero if successful, non-zero otherwise.
> + */
> +__attribute__((unused))
> +static int
> +submit_batch_wi_async(struct buffer_zero_batch_task *batch_task)
> +{
> +    struct dsa_device_group *device_group = batch_task->group;
> +    struct dsa_device *device_instance = batch_task->device;
> +    int ret;
> +
> +    assert(batch_task->task_type == DSA_BATCH_TASK);
> +    assert(batch_task->batch_descriptor.desc_count <= 
> batch_task->batch_size);
> +    assert(batch_task->status == DSA_TASK_READY);
> +
> +    batch_task->status = DSA_TASK_PROCESSING;
> +
> +    ret = submit_wi_int(device_instance->work_queue,
> +                        &batch_task->batch_descriptor);
> +    if (ret != 0)
> +        return ret;
> +
> +    return dsa_task_enqueue(device_group, batch_task);
> +}

At this point in the series submit_wi_async() and
submit_batch_wi_async() look the same to me without the asserts. Can't
we consolidate them?

There's also the fact that both functions receive a _batch_ task but one
is supposed to work in batches and the other is not. That could be
solved by renaming the structure I guess.

> +
>  /**
>   * @brief Check if DSA is running.
>   *
> @@ -301,6 +495,8 @@ void dsa_stop(void)
>      if (!group->running) {
>          return;
>      }
> +
> +    dsa_empty_task_queue(group);
>  }
>  
>  /**