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

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Date:   Fri, 25 Nov 2022 10:16:30 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "lizhijian@...itsu.com" <lizhijian@...itsu.com>
Cc:     "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>,
        "leon@...nel.org" <leon@...nel.org>,
        Bob Pearson <rpearsonhpe@...il.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Mark Bloch <mbloch@...dia.com>, Tom Talpey <tom@...pey.com>,
        "tomasz.gromadzki@...el.com" <tomasz.gromadzki@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "yangx.jy@...itsu.com" <yangx.jy@...itsu.com>,
        "Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [for-next PATCH v6 09/10] RDMA/cm: Make QP FLUSHABLE

On Fri, Nov 25, 2022 at 02:22:24AM +0000, lizhijian@...itsu.com wrote:
> 
> 
> On 25/11/2022 01:39, Jason Gunthorpe wrote:
> > On Wed, Nov 23, 2022 at 06:07:37AM +0000, lizhijian@...itsu.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@...il.com>
> >>>> Signed-off-by: Li Zhijian <lizhijian@...itsu.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