Can I conclude from this that the polling loop (2) from
http://www.mail-archive.com/linux-rdma@vger.kernel.org/msg04907.html
won't trigger a race on a multiprocessor when using mlx4 hardware ?
Bart.
On Tue, Jul 27, 2010 at 11:14 AM, Eli Cohen <e...@dev.mellanox.co.il> wrote:
>
> I don't think this patch is required for mlx4.
>
> < 0 means an error occurred while requesting notification
> == 0 means notification was requested successfully, and if
> IB_CQ_REPORT_MISSED_EVENTS was passed in, then no
> events were missed and it is safe to wait for another
> event.
> > 0 is only returned if IB_CQ_REPORT_MISSED_EVENTS was
> passed in. It means that the consumer must poll the
> CQ again to make sure it is empty to avoid the race
> described above.
>
> returning 1 means that you must poll the CQ to avoid a race condition
> which is not true for mlx4. For example if you return always 0 than
> you don't violate what the changelog says.
>
> On Tue, Jul 27, 2010 at 11:21 AM, Or Gerlitz <ogerl...@voltaire.com> wrote:
> > enhance the cq arming code to support IB_CQ_REPORT_MISSED_EVENTS
> >
> > Signed-off-by: Or Gerlitz <ogerl...@voltaire.com>
> >
> > ----
> >
> > I noted that the IB_CQ_REPORT_MISSED_EVENTS flag was added in the same
> > cycle with mlx4
> > and maybe as of this, mlx4 didn't implement the flag, which is used by IPoIB
> >
> > The patch is compile tested only, if the patch seems okay, I can conduct
> > further testing.
> >
> > diff --git a/drivers/infiniband/hw/mlx4/cq.c
> > b/drivers/infiniband/hw/mlx4/cq.c
> > index 5a219a2..4366811 100644
> > --- a/drivers/infiniband/hw/mlx4/cq.c
> > +++ b/drivers/infiniband/hw/mlx4/cq.c
> > @@ -755,6 +755,13 @@ int mlx4_ib_arm_cq(struct ib_cq *ibcq, enum
> > ib_cq_notify_flags flags)
> > to_mdev(ibcq->device)->uar_map,
> >
> > MLX4_GET_DOORBELL_LOCK(&to_mdev(ibcq->device)->uar_lock));
> >
> > + if (flags & IB_CQ_REPORT_MISSED_EVENTS) {
> > + struct mlx4_cqe *cqe;
> > + cqe = next_cqe_sw(to_mcq(ibcq));
> > + if (cqe)
> > + return 1;
> > + }
> > +
> > return 0;
> > }
> >
> > --
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