On Fri, Aug 16, 2013 at 01:16:27PM +0800, Jason Wang wrote:
> Let vhost_add_used() to use vhost_add_used_n() to reduce the code duplication.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Does compiler inline it then?
Reason I ask, last time I checked put_user inside vhost_add_used
was much cheaper than copy_to_user inside vhost_add_used_n,
so I wouldn't be surprised if this hurt performance.
Did you check?
> ---
> drivers/vhost/vhost.c | 43 ++-----------------------------------------
> 1 files changed, 2 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index e58cf00..c479452 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1332,48 +1332,9 @@ EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);
> * want to notify the guest, using eventfd. */
> int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
> {
> - struct vring_used_elem __user *used;
> + struct vring_used_elem heads = { head, len };
>
> - /* The virtqueue contains a ring of used buffers. Get a pointer to the
> - * next entry in that used ring. */
> - used = &vq->used->ring[vq->last_used_idx % vq->num];
> - if (__put_user(head, &used->id)) {
> - vq_err(vq, "Failed to write used id");
> - return -EFAULT;
> - }
> - if (__put_user(len, &used->len)) {
> - vq_err(vq, "Failed to write used len");
> - return -EFAULT;
> - }
> - /* Make sure buffer is written before we update index. */
> - smp_wmb();
> - if (__put_user(vq->last_used_idx + 1, &vq->used->idx)) {
> - vq_err(vq, "Failed to increment used idx");
> - return -EFAULT;
> - }
> - if (unlikely(vq->log_used)) {
> - /* Make sure data is seen before log. */
> - smp_wmb();
> - /* Log used ring entry write. */
> - log_write(vq->log_base,
> - vq->log_addr +
> - ((void __user *)used - (void __user *)vq->used),
> - sizeof *used);
> - /* Log used index update. */
> - log_write(vq->log_base,
> - vq->log_addr + offsetof(struct vring_used, idx),
> - sizeof vq->used->idx);
> - if (vq->log_ctx)
> - eventfd_signal(vq->log_ctx, 1);
> - }
> - vq->last_used_idx++;
> - /* If the driver never bothers to signal in a very long while,
> - * used index might wrap around. If that happens, invalidate
> - * signalled_used index we stored. TODO: make sure driver
> - * signals at least once in 2^16 and remove this. */
> - if (unlikely(vq->last_used_idx == vq->signalled_used))
> - vq->signalled_used_valid = false;
> - return 0;
> + return vhost_add_used_n(vq, &heads, 1);
> }
> EXPORT_SYMBOL_GPL(vhost_add_used);
>
> --
> 1.7.1
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