On Mon, Dec 28, 2015 at 07:35:14PM -0500, ira.weiny wrote:
>
> I'm still confused. Here is the code with the patch applied:
>
>
> /*
> * IB MAD completion callback
> */
> static void ib_mad_completion_handler(struct work_struct *work)
> {
> struct ib_mad_port_private *port_priv;
> struct ib_wc wc;
> int count = 0;
>
> port_priv = container_of(work, struct ib_mad_port_private, work);
> ib_req_notify_cq(port_priv->cq, IB_CQ_NEXT_COMP);
>
> while (ib_poll_cq(port_priv->cq, 1, &wc) == 1) {
> if (wc.status == IB_WC_SUCCESS) {
> switch (wc.opcode) {
> case IB_WC_SEND:
> ib_mad_send_done_handler(port_priv, &wc);
> break;
> case IB_WC_RECV:
> ib_mad_recv_done_handler(port_priv, &wc);
> break;
> default:
> BUG_ON(1);
> break;
> }
> } else
> mad_error_handler(port_priv, &wc);
>
> if (++count > MAD_COMPLETION_PROC_LIMIT) {
> queue_work(port_priv->wq, &port_priv->work);
> break;
> }
> }
> }
>
>
> How is "return" any different than "break"? Calling return will still result
> in a rearm on the next work task.
My argument is that if you break the loop since you exahsuted the quota you don't need to call ib_req_notify_cq(). If you think about this you will see that this was the original logic of this function. Only after you exhasted the quota you need to call ib_req_notify_cq() so the next completion will trigger the interrupt handler which calls the completion handler. The result is that you are generating less interrupts in the system.
To achieve that you do like this:
/*
* IB MAD completion callback
*/
static void ib_mad_completion_handler(struct work_struct *work)
{
struct ib_mad_port_private *port_priv;
struct ib_wc wc;
int count = 0;
port_priv = container_of(work, struct ib_mad_port_private, work);
while (ib_poll_cq(port_priv->cq, 1, &wc) == 1) {
if (wc.status == IB_WC_SUCCESS) {
switch (wc.opcode) {
case IB_WC_SEND:
ib_mad_send_done_handler(port_priv, &wc);
break;
case IB_WC_RECV:
ib_mad_recv_done_handler(port_priv, &wc);
break;
default:
BUG_ON(1);
break;
}
} else
mad_error_handler(port_priv, &wc);
if (++count > MAD_COMPLETION_PROC_LIMIT) {
queue_work(port_priv->wq, &port_priv->work);
return; <== return and avoid requesting for notification
}
}
ib_req_notify_cq(port_priv->cq, IB_CQ_NEXT_COMP); <== only called if there are no more completions to process
}
I hope my point is clear now.
>
> Perhaps this code is wrong in the first place? Should it call ib_req_notify_cq
> after the while loop? This code has been this way forever...
>
> 1da177e4c3f41 (Linus Torvalds 2005-04-16 15:20:36 -0700 2568) ib_req_notify_cq(port_priv->cq, IB_CQ_NEXT_COMP);
> 1da177e4c3f41 (Linus Torvalds 2005-04-16 15:20:36 -0700 2569)
> 1da177e4c3f41 (Linus Torvalds 2005-04-16 15:20:36 -0700 2570) while (ib_poll_cq(port_priv->cq, 1, &wc) == 1) {
>
>
> Ira
>
>
> >
> > >
> > > I'm not quite sure what you mean about moving the ib_req_notify_cq outside of
> > > the while loop. It seems like to do what you say we would need another work
> > > item which just does ib_poll_cq. Is that what you meant?
> > >
> > > Ira
> > >
> > > >
> > > > > @@ -2574,6 +2587,11 @@ static void ib_mad_completion_handler(struct work_struct *work)
> > > > > }
> > > > > } else
> > > > > mad_error_handler(port_priv, &wc);
> > > > > +
> > > > > + if (++count > MAD_COMPLETION_PROC_LIMIT) {
> > > > > + queue_work(port_priv->wq, &port_priv->work);
> > > > > + break;
> > > > > + }
> > > > > }
> > > > > }
> > > > >
> > > > > --
> > > > > 1.8.2
> > > > >
> > > > > --
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