On Fri, May 07, 2021 at 07:06:34PM +0200, Philippe Mathieu-Daudé wrote:
> By directly using find_first_bit() and find_next_bit from the
> "bitops.h" API to iterate over the bitmap, we can remove the
> bitmap[] variable-length array copy on the stack and the complex
> manual bit testing/clearing logic.
>
> Suggested-by: Stefan Hajnoczi <stefa...@redhat.com>
> Suggested-by: Richard Henderson <richard.hender...@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <phi...@redhat.com>
> ---
> hw/block/dataplane/virtio-blk.c | 19 ++++---------------
> 1 file changed, 4 insertions(+), 15 deletions(-)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index e9050c8987e..a7b5bda06fc 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -60,23 +60,12 @@ static void notify_guest_bh(void *opaque)
> {
> VirtIOBlockDataPlane *s = opaque;
> unsigned nvqs = s->conf->num_queues;
> - unsigned long bitmap[BITS_TO_LONGS(nvqs)];
> - unsigned j;
>
> - memcpy(bitmap, s->batch_notify_vqs, sizeof(bitmap));
> - memset(s->batch_notify_vqs, 0, sizeof(bitmap));
> + for (unsigned long i = find_first_bit(s->batch_notify_vqs, nvqs);
> + i < nvqs; i = find_next_bit(s->batch_notify_vqs, nvqs, i)) {
> + VirtQueue *vq = virtio_get_queue(s->vdev, i);
>
> - for (j = 0; j < nvqs; j += BITS_PER_LONG) {
> - unsigned long bits = bitmap[j / BITS_PER_LONG];
> -
> - while (bits != 0) {
> - unsigned i = j + ctzl(bits);
> - VirtQueue *vq = virtio_get_queue(s->vdev, i);
> -
> - virtio_notify_irqfd(s->vdev, vq);
> -
> - bits &= bits - 1; /* clear right-most bit */
> - }
> + virtio_notify_irqfd(s->vdev, vq);
> }
> }Bits in s->batch_notify_vqs[] must be cleared. Otherwise we may raise spurious irqs next time this function is called. The memset() can be moved after the loop. Stefan
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