Re: [PATCH 2/3] vdpa_sim_blk: limit the number of request handled per batch

[Jason Wang]

On Thu, Jun 23, 2022 at 4:58 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
>
> On Thu, Jun 23, 2022 at 11:50:22AM +0800, Jason Wang wrote:
> >On Wed, Jun 22, 2022 at 12:09 AM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
> >>
> >> Limit the number of requests (4 per queue as for vdpa_sim_net) handled
> >> in a batch to prevent the worker from using the CPU for too long.
> >>
> >> Suggested-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> >> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> >> ---
> >>  drivers/vdpa/vdpa_sim/vdpa_sim_blk.c | 15 ++++++++++++++-
> >>  1 file changed, 14 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> >> index a83a5c76f620..ac86478845b6 100644
> >> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> >> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> >> @@ -197,6 +197,7 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
> >>  static void vdpasim_blk_work(struct work_struct *work)
> >>  {
> >>         struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
> >> +       bool reschedule = false;
> >>         int i;
> >>
> >>         spin_lock(&vdpasim->lock);
> >> @@ -206,11 +207,15 @@ static void vdpasim_blk_work(struct work_struct *work)
> >>
> >>         for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
> >>                 struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
> >> +               bool vq_work = true;
> >> +               int reqs = 0;
> >>
> >>                 if (!vq->ready)
> >>                         continue;
> >>
> >> -               while (vdpasim_blk_handle_req(vdpasim, vq)) {
> >> +               while (vq_work) {
> >> +                       vq_work = vdpasim_blk_handle_req(vdpasim, vq);
> >> +
> >
> >Is it better to check and exit the loop early here?
>
> Maybe, but I'm not sure.
>
> In vdpa_sim_net we call vringh_complete_iotlb() and send notification
> also in the error path,

Looks not?

                read = vringh_iov_pull_iotlb(&cvq->vring, &cvq->in_iov, &ctrl,
                                             sizeof(ctrl));
                if (read != sizeof(ctrl))
                        break;

We break the loop.

Thanks

> so I thought was better to send notification
> also when vdpasim_blk_handle_req() return false, since we will update
> the used.idx.
>
> However, I don't think it's a common path, so if you think it's better
> to exit the loop early, I can do it.
>
> Thanks,
> Stefano
>