Hi Rusty,
On Tue, Jan 28, 2014 at 10:48:31AM +1030, Rusty Russell wrote:
> Leandro Dorileo <l@xxxxxxxxxxx> writes:
> > Cchange init_vqs() to avoid calling twice the virtio_has_feature()
> > - attempting to find out if VIRTIO_BALLOON_F_STATS_VQ feature was negotiated -
> > consequently we prevent unnecessarily running the drivers' feature_table more
> > than needed.
> >
> > Signed-off-by: Leandro Dorileo <l@xxxxxxxxxxx>
>
> Hi Leandro,
>
> This seems like a premature optimization. The current code is
> fairly clear, and there's no performance issue with init_vqs.
>
Indeed, rethinking the patch and reviewing the code path it seems to be no gain,
It's just called on probe and restore operations. As you said a premature optimization.
Thanks...
> Am I missing something?
> Rusty.
>
> > ---
> > drivers/virtio/virtio_balloon.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index 34bdaba..41771c1 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -320,19 +320,21 @@ static int init_vqs(struct virtio_balloon *vb)
> > vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
> > const char *names[] = { "inflate", "deflate", "stats" };
> > int err, nvqs;
> > + bool stats;
> >
> > /*
> > * We expect two virtqueues: inflate and deflate, and
> > * optionally stat.
> > */
> > - nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
> > + stats = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ);
> > + nvqs = stats ? 3 : 2;
> > err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
> > if (err)
> > return err;
> >
> > vb->inflate_vq = vqs[0];
> > vb->deflate_vq = vqs[1];
> > - if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> > + if (stats) {
> > struct scatterlist sg;
> > vb->stats_vq = vqs[2];
> >
> > --
> > 1.8.5.3
> --
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--
Leandro Dorileo
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