Re: [PATCH v1 06/10] svcrdma: Plant reader function in struct svcxprt_rdma

[Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On 1/9/2015 9:22 PM, Chuck Lever wrote:
> The RDMA reader function doesn't change once an svcxprt is
> instantiated. Instead of checking sc_devcap during every incoming
> RPC, set the reader function once when the connection is accepted.
>

General question(s),

Any specific reason why to use FRMR in the server side? And why only
for reads and not writes? Sorry if these are dumb questions...

Sagi.

> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
>
>   include/linux/sunrpc/svc_rdma.h          |   10 ++++
>   net/sunrpc/xprtrdma/svc_rdma_recvfrom.c  |   71 +++++++++++-------------------
>   net/sunrpc/xprtrdma/svc_rdma_transport.c |    2 +
>   3 files changed, 39 insertions(+), 44 deletions(-)
>
> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> index 2280325..f161e30 100644
> --- a/include/linux/sunrpc/svc_rdma.h
> +++ b/include/linux/sunrpc/svc_rdma.h
> @@ -150,6 +150,10 @@ struct svcxprt_rdma {
>   	struct ib_cq         *sc_rq_cq;
>   	struct ib_cq         *sc_sq_cq;
>   	struct ib_mr         *sc_phys_mr;	/* MR for server memory */
> +	int		     (*sc_reader)(struct svcxprt_rdma *,
> +					  struct svc_rqst *,
> +					  struct svc_rdma_op_ctxt *,
> +					  int *, u32 *, u32, u32, u64, bool);
>   	u32		     sc_dev_caps;	/* distilled device caps */
>   	u32		     sc_dma_lkey;	/* local dma key */
>   	unsigned int	     sc_frmr_pg_list_len;
> @@ -195,6 +199,12 @@ extern int svc_rdma_xdr_get_reply_hdr_len(struct rpcrdma_msg *);
>
>   /* svc_rdma_recvfrom.c */
>   extern int svc_rdma_recvfrom(struct svc_rqst *);
> +extern int rdma_read_chunk_lcl(struct svcxprt_rdma *, struct svc_rqst *,
> +			       struct svc_rdma_op_ctxt *, int *, u32 *,
> +			       u32, u32, u64, bool);
> +extern int rdma_read_chunk_frmr(struct svcxprt_rdma *, struct svc_rqst *,
> +				struct svc_rdma_op_ctxt *, int *, u32 *,
> +				u32, u32, u64, bool);
>
>   /* svc_rdma_sendto.c */
>   extern int svc_rdma_sendto(struct svc_rqst *);
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index 577f865..c3aebc1 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -117,26 +117,16 @@ static int rdma_read_max_sge(struct svcxprt_rdma *xprt, int sge_count)
>   		return min_t(int, sge_count, xprt->sc_max_sge);
>   }
>
> -typedef int (*rdma_reader_fn)(struct svcxprt_rdma *xprt,
> -			      struct svc_rqst *rqstp,
> -			      struct svc_rdma_op_ctxt *head,
> -			      int *page_no,
> -			      u32 *page_offset,
> -			      u32 rs_handle,
> -			      u32 rs_length,
> -			      u64 rs_offset,
> -			      int last);
> -
>   /* Issue an RDMA_READ using the local lkey to map the data sink */
> -static int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
> -			       struct svc_rqst *rqstp,
> -			       struct svc_rdma_op_ctxt *head,
> -			       int *page_no,
> -			       u32 *page_offset,
> -			       u32 rs_handle,
> -			       u32 rs_length,
> -			       u64 rs_offset,
> -			       int last)
> +int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
> +			struct svc_rqst *rqstp,
> +			struct svc_rdma_op_ctxt *head,
> +			int *page_no,
> +			u32 *page_offset,
> +			u32 rs_handle,
> +			u32 rs_length,
> +			u64 rs_offset,
> +			bool last)
>   {
>   	struct ib_send_wr read_wr;
>   	int pages_needed = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
> @@ -221,15 +211,15 @@ static int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
>   }
>
>   /* Issue an RDMA_READ using an FRMR to map the data sink */
> -static int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
> -				struct svc_rqst *rqstp,
> -				struct svc_rdma_op_ctxt *head,
> -				int *page_no,
> -				u32 *page_offset,
> -				u32 rs_handle,
> -				u32 rs_length,
> -				u64 rs_offset,
> -				int last)
> +int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
> +			 struct svc_rqst *rqstp,
> +			 struct svc_rdma_op_ctxt *head,
> +			 int *page_no,
> +			 u32 *page_offset,
> +			 u32 rs_handle,
> +			 u32 rs_length,
> +			 u64 rs_offset,
> +			 bool last)
>   {
>   	struct ib_send_wr read_wr;
>   	struct ib_send_wr inv_wr;
> @@ -374,9 +364,9 @@ static int rdma_read_chunks(struct svcxprt_rdma *xprt,
>   {
>   	int page_no, ret;
>   	struct rpcrdma_read_chunk *ch;
> -	u32 page_offset, byte_count;
> +	u32 handle, page_offset, byte_count;
>   	u64 rs_offset;
> -	rdma_reader_fn reader;
> +	bool last;
>
>   	/* If no read list is present, return 0 */
>   	ch = svc_rdma_get_read_chunk(rmsgp);
> @@ -399,27 +389,20 @@ static int rdma_read_chunks(struct svcxprt_rdma *xprt,
>   	head->arg.len = rqstp->rq_arg.len;
>   	head->arg.buflen = rqstp->rq_arg.buflen;
>
> -	/* Use FRMR if supported */
> -	if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_FAST_REG)
> -		reader = rdma_read_chunk_frmr;
> -	else
> -		reader = rdma_read_chunk_lcl;
> -
>   	page_no = 0; page_offset = 0;
>   	for (ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
>   	     ch->rc_discrim != 0; ch++) {
> -
> +		handle = be32_to_cpu(ch->rc_target.rs_handle);
> +		byte_count = be32_to_cpu(ch->rc_target.rs_length);
>   		xdr_decode_hyper((__be32 *)&ch->rc_target.rs_offset,
>   				 &rs_offset);
> -		byte_count = ntohl(ch->rc_target.rs_length);
>
>   		while (byte_count > 0) {
> -			ret = reader(xprt, rqstp, head,
> -				     &page_no, &page_offset,
> -				     ntohl(ch->rc_target.rs_handle),
> -				     byte_count, rs_offset,
> -				     ((ch+1)->rc_discrim == 0) /* last */
> -				     );
> +			last = (ch + 1)->rc_discrim == xdr_zero;
> +			ret = xprt->sc_reader(xprt, rqstp, head,
> +					      &page_no, &page_offset,
> +					      handle, byte_count,
> +					      rs_offset, last);
>   			if (ret < 0)
>   				goto err;
>   			byte_count -= ret;
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> index f2e059b..f609c1c 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> @@ -974,10 +974,12 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>   	 * NB:	iWARP requires remote write access for the data sink
>   	 *	of an RDMA_READ. IB does not.
>   	 */
> +	newxprt->sc_reader = rdma_read_chunk_lcl;
>   	if (devattr.device_cap_flags & IB_DEVICE_MEM_MGT_EXTENSIONS) {
>   		newxprt->sc_frmr_pg_list_len =
>   			devattr.max_fast_reg_page_list_len;
>   		newxprt->sc_dev_caps |= SVCRDMA_DEVCAP_FAST_REG;
> +		newxprt->sc_reader = rdma_read_chunk_frmr;
>   	}
>
>   	/*
>
> --
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