[ofa-general] [Bug 508] IPoIB CM multicast is hogging interrupts

[Michael S. Tsirkin]

Quoting Pradeep Satyanarayana <pradeep at us.ibm.com>:
Subject: Re: [ofa-general] [Bug 508] IPoIB CM multicast is hogging interrupts

> I think this trick I just came up with is a simpe way to prevent
> IPoIB TX from hogging interrupts, even without NAPI. And it might be a better
> way to solve the problem for IPoIB CM TX than using a common cq
> as my previous patch did.
> >  static void ipoib_cm_tx_completion(struct ib_cq *cq, void *tx_ptr)
> >  {
> >     struct ipoib_cm_tx *tx = tx_ptr;
> > -   int n, i;
> > +   int n, i, cnt = 0;
> > 
> >     ib_req_notify_cq(cq, IB_CQ_NEXT_COMP);
> >     do {
> >        n = ib_poll_cq(cq, IPOIB_NUM_WC, tx->ibwc);
> > +      cnt += n;
> >        for (i = 0; i < n; ++i)
> >           ipoib_cm_handle_tx_wc(tx->dev, tx, tx->ibwc + i);
> > -   } while (n == IPOIB_NUM_WC);
> > +   } while (n == IPOIB_NUM_WC && cnt < ipoib_sendq_size);
> >  }
> 
> This change might exit tx_completion sooner -how does that prevent
> hogging interrupts (without NAPI)? I am not clear about that.

By returning from interrupt handler after a finite number of
completions, rather than polling CQ potentially indefinitely.

-- 
MST