Re: [for-next PATCH v6 09/10] RDMA/cm: Make QP FLUSHABLE

Jason Gunthorpe
2022-11-25T14:16:36Z

On Fri, Nov 25, 2022 at 02:22:24AM +0000, lizhijian@fujitsu.com wrote:
>
>
> On 25/11/2022 01:39, Jason Gunthorpe wrote:
> > On Wed, Nov 23, 2022 at 06:07:37AM +0000, lizhijian@fujitsu.com wrote:
> >>
> >>
> >> On 22/11/2022 22:52, Jason Gunthorpe wrote:
> >>> On Wed, Nov 16, 2022 at 04:19:50PM +0800, Li Zhijian wrote:
> >>>> It enables flushable access flag for qp
> >>>>
> >>>> Reviewed-by: Zhu Yanjun <zyjzyj2000@gmail.com>
> >>>> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> >>>> ---
> >>>> V5: new patch, inspired by Bob
> >>>> ---
> >>>> drivers/infiniband/core/cm.c | 3 ++-
> >>>> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> >>>> index 1f9938a2c475..58837aac980b 100644
> >>>> --- a/drivers/infiniband/core/cm.c
> >>>> +++ b/drivers/infiniband/core/cm.c
> >>>> @@ -4096,7 +4096,8 @@ static int cm_init_qp_init_attr(struct cm_id_private *cm_id_priv,
> >>>> qp_attr->qp_access_flags = IB_ACCESS_REMOTE_WRITE;
> >>>> if (cm_id_priv->responder_resources)
> >>>> qp_attr->qp_access_flags |= IB_ACCESS_REMOTE_READ |
> >>>> - IB_ACCESS_REMOTE_ATOMIC;
> >>>> + IB_ACCESS_REMOTE_ATOMIC |
> >>>> + IB_ACCESS_FLUSHABLE;
> >>>
> >>> What is the point of this? Nothing checks IB_ACCESS_FLUSHABLE ?
> >>
> >> Previous, responder of RXE will check qp_access_flags in check_op_valid():
> >> 256 static enum resp_states check_op_valid(struct rxe_qp *qp,
> >>
> >> 257 struct rxe_pkt_info *pkt)
> >>
> >> 258 {
> >>
> >> 259 switch (qp_type(qp)) {
> >>
> >> 260 case IB_QPT_RC:
> >>
> >> 261 if (((pkt->mask & RXE_READ_MASK) &&
> >>
> >> 262 !(qp->attr.qp_access_flags &
> >> IB_ACCESS_REMOTE_READ)) ||
> >>
> >>
> >> 263 ((pkt->mask & RXE_WRITE_MASK) &&
> >>
> >> 264 !(qp->attr.qp_access_flags &
> >> IB_ACCESS_REMOTE_WRITE)) ||
> >> 265 ((pkt->mask & RXE_ATOMIC_MASK) &&
> >>
> >> 266 !(qp->attr.qp_access_flags &
> >> IB_ACCESS_REMOTE_ATOMIC))) {
> >> 267 return RESPST_ERR_UNSUPPORTED_OPCODE;
> >>
> >> 268 }
> >>
> >> based on this, additional IB_FLUSH_PERSISTENT and IB_ACCESS_FLUSH_GLOBAL
> >> were added in patch7 since V5 suggested by Bob.
> >> Because of this change, QP should become FLUSHABLE correspondingly.
> >
> > But nothing ever reads IB_ACCESS_FLUSHABLE, so why is it added?
>
> include/rdma/ib_verbs.h:
> + IB_ACCESS_FLUSH_GLOBAL = IB_UVERBS_ACCESS_FLUSH_GLOBAL,
> + IB_ACCESS_FLUSH_PERSISTENT = IB_UVERBS_ACCESS_FLUSH_PERSISTENT,
> + IB_ACCESS_FLUSHABLE = IB_ACCESS_FLUSH_GLOBAL |
> + IB_ACCESS_FLUSH_PERSISTENT,
>
> IB_ACCESS_FLUSHABLE is a wrapper of IB_ACCESS_FLUSH_GLOBAL |
> IB_ACCESS_FLUSH_PERSISTENT. With this wrapper, i will write one less
> line of code :)
>
> I'm fine to expand it in next version.

OIC, that is why it escaped grep

But this is back to my original question - why is it OK to do this
here in CMA? Shouldn't this cause other drivers to refuse to create
the QP because they don't support the flag?

Jason

>
> >
> > Jason