Re: [PATCH v1 2/8] svcrdma: Define maximum number of backchannel requests

[Tom Talpey <tom@talpey.com>]

On 11/23/2015 5:20 PM, Chuck Lever wrote:
> Extra resources for handling backchannel requests have to be
> pre-allocated when a transport instance is created. Set a limit.
>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>   include/linux/sunrpc/svc_rdma.h          |    5 +++++
>   net/sunrpc/xprtrdma/svc_rdma_transport.c |    6 +++++-
>   2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> index f869807..478aa30 100644
> --- a/include/linux/sunrpc/svc_rdma.h
> +++ b/include/linux/sunrpc/svc_rdma.h
> @@ -178,6 +178,11 @@ struct svcxprt_rdma {
>   #define RPCRDMA_SQ_DEPTH_MULT   8
>   #define RPCRDMA_MAX_REQUESTS    32
>   #define RPCRDMA_MAX_REQ_SIZE    4096
> +#if defined(CONFIG_SUNRPC_BACKCHANNEL)

Why is this a config option? Why wouldn't you always want
this? It's needed for any post-1990 NFS dialect.

> +#define RPCRDMA_MAX_BC_REQUESTS	8

Why a constant 8? The forward channel value is apparently
configurable, just a few lines down.

> +#else
> +#define RPCRDMA_MAX_BC_REQUESTS	0
> +#endif
>
>   #define RPCSVC_MAXPAYLOAD_RDMA	RPCSVC_MAXPAYLOAD
>
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> index b348b4a..01c7b36 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> @@ -923,8 +923,10 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>   				  (size_t)RPCSVC_MAXPAGES);
>   	newxprt->sc_max_sge_rd = min_t(size_t, devattr.max_sge_rd,
>   				       RPCSVC_MAXPAGES);
> +	/* XXX: what if HCA can't support enough WRs for bc operation? */
>   	newxprt->sc_max_requests = min((size_t)devattr.max_qp_wr,
> -				   (size_t)svcrdma_max_requests);
> +				       (size_t)(svcrdma_max_requests +
> +				       RPCRDMA_MAX_BC_REQUESTS));
>   	newxprt->sc_sq_depth = RPCRDMA_SQ_DEPTH_MULT * newxprt->sc_max_requests;
>
>   	/*
> @@ -964,7 +966,9 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>   	qp_attr.event_handler = qp_event_handler;
>   	qp_attr.qp_context = &newxprt->sc_xprt;
>   	qp_attr.cap.max_send_wr = newxprt->sc_sq_depth;
> +	qp_attr.cap.max_send_wr += RPCRDMA_MAX_BC_REQUESTS;
>   	qp_attr.cap.max_recv_wr = newxprt->sc_max_requests;
> +	qp_attr.cap.max_recv_wr += RPCRDMA_MAX_BC_REQUESTS;
>   	qp_attr.cap.max_send_sge = newxprt->sc_max_sge;
>   	qp_attr.cap.max_recv_sge = newxprt->sc_max_sge;
>   	qp_attr.sq_sig_type = IB_SIGNAL_REQ_WR;
>
> --
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