Re: [PATCH v2 11/20] util/dsa: Implement DSA task asynchronous submission and wait for completion.

[Fabiano Rosas]

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

> * Add a DSA task completion callback.
> * DSA completion thread will call the tasks's completion callback
> on every task/batch task completion.
> * DSA submission path to wait for completion.
> * Implement CPU fallback if DSA is not able to complete the task.
>
> Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
> Signed-off-by: Bryan Zhang <bryan.zhang@bytedance.com>
> ---
>  include/qemu/dsa.h |  14 +++++
>  util/dsa.c         | 153 ++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 164 insertions(+), 3 deletions(-)
>
> diff --git a/include/qemu/dsa.h b/include/qemu/dsa.h
> index b10e7b8fb7..3f8ee07004 100644
> --- a/include/qemu/dsa.h
> +++ b/include/qemu/dsa.h
> @@ -65,6 +65,20 @@ void buffer_zero_batch_task_init(struct 
> buffer_zero_batch_task *task,
>   */
>  void buffer_zero_batch_task_destroy(struct buffer_zero_batch_task *task);
>  
> +/**
> + * @brief Performs buffer zero comparison on a DSA batch task asynchronously.
> + *
> + * @param batch_task A pointer to the batch task.
> + * @param buf An array of memory buffers.
> + * @param count The number of buffers in the array.
> + * @param len The buffer length.
> + *
> + * @return Zero if successful, otherwise non-zero.
> + */
> +int
> +buffer_is_zero_dsa_batch_async(struct buffer_zero_batch_task *batch_task,
> +                               const void **buf, size_t count, size_t len);
> +
>  /**
>   * @brief Initializes DSA devices.
>   *
> diff --git a/util/dsa.c b/util/dsa.c
> index 3cc017b8a0..06c6fbf2ca 100644
> --- a/util/dsa.c
> +++ b/util/dsa.c
> @@ -470,6 +470,41 @@ poll_completion(struct dsa_completion_record *completion,
>      return 0;
>  }
>  
> +/**
> + * @brief Use CPU to complete a single zero page checking task.
> + *
> + * @param task A pointer to the task.
> + */
> +static void
> +task_cpu_fallback(struct buffer_zero_batch_task *task)
> +{
> +    assert(task->task_type == DSA_TASK);
> +
> +    struct dsa_completion_record *completion = &task->completions[0];
> +    const uint8_t *buf;
> +    size_t len;
> +
> +    if (completion->status == DSA_COMP_SUCCESS) {
> +        return;
> +    }
> +
> +    /*
> +     * DSA was able to partially complete the operation. Check the
> +     * result. If we already know this is not a zero page, we can
> +     * return now.
> +     */
> +    if (completion->bytes_completed != 0 && completion->result != 0) {
> +        task->results[0] = false;
> +        return;
> +    }
> +
> +    /* Let's fallback to use CPU to complete it. */
> +    buf = (const uint8_t *)task->descriptors[0].src_addr;
> +    len = task->descriptors[0].xfer_size;
> +    task->results[0] = buffer_is_zero(buf + completion->bytes_completed,
> +                                      len - completion->bytes_completed);
> +}
> +
>  /**
>   * @brief Complete a single DSA task in the batch task.
>   *
> @@ -548,6 +583,62 @@ poll_batch_task_completion(struct buffer_zero_batch_task 
> *batch_task)
>      }
>  }
>  
> +/**
> + * @brief Use CPU to complete the zero page checking batch task.
> + *
> + * @param batch_task A pointer to the batch task.
> + */
> +static void
> +batch_task_cpu_fallback(struct buffer_zero_batch_task *batch_task)
> +{
> +    assert(batch_task->task_type == DSA_BATCH_TASK);
> +
> +    struct dsa_completion_record *batch_completion =
> +        &batch_task->batch_completion;
> +    struct dsa_completion_record *completion;
> +    uint8_t status;
> +    const uint8_t *buf;
> +    size_t len;
> +    bool *results = batch_task->results;
> +    uint32_t count = batch_task->batch_descriptor.desc_count;
> +
> +    // DSA is able to complete the entire batch task.
> +    if (batch_completion->status == DSA_COMP_SUCCESS) {
> +        assert(count == batch_completion->bytes_completed);
> +        return;
> +    }
> +
> +    /*
> +     * DSA encounters some error and is not able to complete
> +     * the entire batch task. Use CPU fallback.
> +     */
> +    for (int i = 0; i < count; i++) {
> +        completion = &batch_task->completions[i];
> +        status = completion->status;
> +        if (status == DSA_COMP_SUCCESS) {
> +            continue;
> +        }
> +        assert(status == DSA_COMP_PAGE_FAULT_NOBOF);
> +
> +        /*
> +         * DSA was able to partially complete the operation. Check the
> +         * result. If we already know this is not a zero page, we can
> +         * return now.
> +         */
> +        if (completion->bytes_completed != 0 && completion->result != 0) {
> +            results[i] = false;
> +            continue;
> +        }
> +
> +        /* Let's fallback to use CPU to complete it. */
> +        buf = (uint8_t *)batch_task->descriptors[i].src_addr;
> +        len = batch_task->descriptors[i].xfer_size;
> +        results[i] =
> +            buffer_is_zero(buf + completion->bytes_completed,
> +                           len - completion->bytes_completed);

Here the same thing is happening as in other patches, the batch task
operation is just a repeat of the task operation n times. So this whole
inner code here could be nicely replaced by task_cpu_fallback() with
some adjustment of the function arguments. That makes intuitive sense
and removes code duplication.

> +    }
> +}
> +
>  /**
>   * @brief Handles an asynchronous DSA batch task completion.
>   *
> @@ -825,7 +916,6 @@ buffer_zero_batch_task_set(struct buffer_zero_batch_task 
> *batch_task,
>   *
>   * @return int Zero if successful, otherwise an appropriate error code.
>   */
> -__attribute__((unused))
>  static int
>  buffer_zero_dsa_async(struct buffer_zero_batch_task *task,
>                        const void *buf, size_t len)
> @@ -844,7 +934,6 @@ buffer_zero_dsa_async(struct buffer_zero_batch_task *task,
>   * @param count The number of buffers.
>   * @param len The buffer length.
>   */
> -__attribute__((unused))
>  static int
>  buffer_zero_dsa_batch_async(struct buffer_zero_batch_task *batch_task,
>                              const void **buf, size_t count, size_t len)
> @@ -876,13 +965,29 @@ buffer_zero_dsa_completion(void *context)
>   *
>   * @param batch_task A pointer to the buffer zero comparison batch task.
>   */
> -__attribute__((unused))
>  static void
>  buffer_zero_dsa_wait(struct buffer_zero_batch_task *batch_task)
>  {
>      qemu_sem_wait(&batch_task->sem_task_complete);
>  }
>  
> +/**
> + * @brief Use CPU to complete the zero page checking task if DSA
> + *        is not able to complete it.
> + *
> + * @param batch_task A pointer to the batch task.
> + */
> +static void
> +buffer_zero_cpu_fallback(struct buffer_zero_batch_task *batch_task)
> +{
> +    if (batch_task->task_type == DSA_TASK) {
> +        task_cpu_fallback(batch_task);
> +    } else {
> +        assert(batch_task->task_type == DSA_BATCH_TASK);
> +        batch_task_cpu_fallback(batch_task);
> +    }
> +}
> +
>  /**
>   * @brief Check if DSA is running.
>   *
> @@ -956,6 +1061,41 @@ void dsa_cleanup(void)
>      dsa_device_group_cleanup(&dsa_group);
>  }
>  
> +/**
> + * @brief Performs buffer zero comparison on a DSA batch task asynchronously.
> + *
> + * @param batch_task A pointer to the batch task.
> + * @param buf An array of memory buffers.
> + * @param count The number of buffers in the array.
> + * @param len The buffer length.
> + *
> + * @return Zero if successful, otherwise non-zero.
> + */
> +int
> +buffer_is_zero_dsa_batch_async(struct buffer_zero_batch_task *batch_task,
> +                               const void **buf, size_t count, size_t len)
> +{
> +    if (count <= 0 || count > batch_task->batch_size) {
> +        return -1;
> +    }
> +
> +    assert(batch_task != NULL);
> +    assert(len != 0);
> +    assert(buf != NULL);
> +
> +    if (count == 1) {
> +        // DSA doesn't take batch operation with only 1 task.
> +        buffer_zero_dsa_async(batch_task, buf[0], len);
> +    } else {
> +        buffer_zero_dsa_batch_async(batch_task, buf, count, len);
> +    }
> +
> +    buffer_zero_dsa_wait(batch_task);
> +    buffer_zero_cpu_fallback(batch_task);
> +
> +    return 0;
> +}
> +
>  #else
>  
>  void buffer_zero_batch_task_init(struct buffer_zero_batch_task *task,
> @@ -981,5 +1121,12 @@ void dsa_stop(void) {}
>  
>  void dsa_cleanup(void) {}
>  
> +int
> +buffer_is_zero_dsa_batch_async(struct buffer_zero_batch_task *batch_task,
> +                               const void **buf, size_t count, size_t len)
> +{
> +    exit(1);
> +}
> +
>  #endif