On Wed, Oct 27, 2021 at 02:19:11PM +0800, Xuan Zhuo wrote:
> In the case of using indirect, indirect desc must be allocated and
> released each time, which increases a lot of cpu overhead.
>
> Here, a cache is added for indirect. If the number of indirect desc to be
> applied for is less than VIRT_QUEUE_CACHE_DESC_NUM, the desc array with
> the size of VIRT_QUEUE_CACHE_DESC_NUM is fixed and cached for reuse.
>
> Signed-off-by: Xuan Zhuo <xuanz...@linux.alibaba.com>
> ---
> drivers/virtio/virtio.c | 6 ++++
> drivers/virtio/virtio_ring.c | 63 ++++++++++++++++++++++++++++++------
> include/linux/virtio.h | 10 ++++++
> 3 files changed, 70 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 0a5b54034d4b..04bcb74e5b9a 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -431,6 +431,12 @@ bool is_virtio_device(struct device *dev)
> }
> EXPORT_SYMBOL_GPL(is_virtio_device);
>
> +void virtio_use_desc_cache(struct virtio_device *dev, bool val)
> +{
> + dev->desc_cache = val;
> +}
> +EXPORT_SYMBOL_GPL(virtio_use_desc_cache);
> +
> void unregister_virtio_device(struct virtio_device *dev)
> {
> int index = dev->index; /* save for after device release */
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index dd95dfd85e98..0b9a8544b0e8 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -117,6 +117,10 @@ struct vring_virtqueue {
> /* Hint for event idx: already triggered no need to disable. */
> bool event_triggered;
>
> + /* Is indirect cache used? */
> + bool use_desc_cache;
> + void *desc_cache_chain;
> +
> union {
> /* Available for split ring */
> struct {
> @@ -423,12 +427,47 @@ static unsigned int vring_unmap_one_split(const struct
> vring_virtqueue *vq,
> return extra[i].next;
> }
>
> -static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
> +#define VIRT_QUEUE_CACHE_DESC_NUM 4
> +
> +static void desc_cache_chain_free_split(void *chain)
> +{
> + struct vring_desc *desc;
> +
> + while (chain) {
> + desc = chain;
> + chain = (void *)desc->addr;
> + kfree(desc);
> + }
> +}
> +
> +static void desc_cache_put_split(struct vring_virtqueue *vq,
> + struct vring_desc *desc, int n)
> +{
> + if (vq->use_desc_cache && n <= VIRT_QUEUE_CACHE_DESC_NUM) {
> + desc->addr = (u64)vq->desc_cache_chain;
> + vq->desc_cache_chain = desc;
> + } else {
> + kfree(desc);
> + }
> +}
> +
So I have a question here. What happens if we just do:
if (n <= VIRT_QUEUE_CACHE_DESC_NUM) {
return kmem_cache_alloc(VIRT_QUEUE_CACHE_DESC_NUM * sizeof desc, gfp)
} else {
return kmalloc_arrat(n, sizeof desc, gfp)
}
A small change and won't we reap most performance benefits?
--
MST
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