Return-Path: Received: from mx143.netapp.com ([216.240.21.24]:20784 "EHLO mx143.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756977AbcH2OYJ (ORCPT ); Mon, 29 Aug 2016 10:24:09 -0400 From: Anna Schumaker Subject: Re: [PATCH v2 05/22] SUNRPC: Separate buffer pointers for RPC Call and Reply messages To: Chuck Lever , , References: <20160823174402.13038.84561.stgit@manet.1015granger.net> <20160823175244.13038.39619.stgit@manet.1015granger.net> Message-ID: <1e9440d8-111a-4252-c706-2e3c26f7b09a@Netapp.com> Date: Mon, 29 Aug 2016 10:23:47 -0400 MIME-Version: 1.0 In-Reply-To: <20160823175244.13038.39619.stgit@manet.1015granger.net> Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: Hi Chuck, On 08/23/2016 01:52 PM, Chuck Lever wrote: > For xprtrdma, the RPC Call and Reply buffers are involved in real > I/O operations. > > To start with, the DMA direction of the I/O for a Call is opposite > that of a Reply. > > In the current arrangement, the Reply buffer address is on a > four-byte alignment just past the call buffer. Would be friendlier > on some platforms if that was at a DMA cache alignment instead. > > Because the current arrangement allocates a single memory region > which contains both buffers, the RPC Reply buffer often contains a > page boundary in it when the Call buffer is large enough (which is > frequent). > > It would be a little nicer for setting up DMA operations (and > possible registration of the Reply buffer) if the two buffers were > separated, well-aligned, and contained as few page boundaries as > possible. > > Now, I could just pad out the single memory region used for the pair > of buffers. But frequently that would mean a lot of unused space to > ensure the Reply buffer did not have a page boundary. > > Add a separate pointer to rpc_rqst that points right to the RPC > Reply buffer. This makes no difference to xprtsock, but it will help > xprtrdma in subsequent patches. > > Signed-off-by: Chuck Lever > --- > include/linux/sunrpc/xprt.h | 5 +++-- > net/sunrpc/clnt.c | 2 +- > net/sunrpc/sched.c | 1 + > net/sunrpc/xprtrdma/transport.c | 1 + > 4 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h > index 72c2aeb..46f069e 100644 > --- a/include/linux/sunrpc/xprt.h > +++ b/include/linux/sunrpc/xprt.h > @@ -84,8 +84,9 @@ struct rpc_rqst { > struct list_head rq_list; > > void *rq_buffer; /* Call XDR encode buffer */ > - size_t rq_callsize, > - rq_rcvsize; > + size_t rq_callsize; > + void *rq_rbuffer; /* Reply XDR decode buffer */ > + size_t rq_rcvsize; Just a nit-picky question :) Is there any reason that you're adding the buffer between rq_callsize and rq_rcvsize? It seems like you could leave those alone and add the pointer either before or after them. Thanks, Anna > size_t rq_xmit_bytes_sent; /* total bytes sent */ > size_t rq_reply_bytes_recvd; /* total reply bytes */ > /* received */ > diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c > index ab467c0..fd389c0 100644 > --- a/net/sunrpc/clnt.c > +++ b/net/sunrpc/clnt.c > @@ -1768,7 +1768,7 @@ rpc_xdr_encode(struct rpc_task *task) > req->rq_buffer, > req->rq_callsize); > xdr_buf_init(&req->rq_rcv_buf, > - (char *)req->rq_buffer + req->rq_callsize, > + req->rq_rbuffer, > req->rq_rcvsize); > > p = rpc_encode_header(task); > diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c > index 6690ebc..5db68b3 100644 > --- a/net/sunrpc/sched.c > +++ b/net/sunrpc/sched.c > @@ -891,6 +891,7 @@ int rpc_malloc(struct rpc_task *task) > dprintk("RPC: %5u allocated buffer of size %zu at %p\n", > task->tk_pid, size, buf); > rqst->rq_buffer = buf->data; > + rqst->rq_rbuffer = (char *)rqst->rq_buffer + rqst->rq_callsize; > return 0; > } > EXPORT_SYMBOL_GPL(rpc_malloc); > diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c > index ebf14ba..136caf3 100644 > --- a/net/sunrpc/xprtrdma/transport.c > +++ b/net/sunrpc/xprtrdma/transport.c > @@ -524,6 +524,7 @@ out: > dprintk("RPC: %s: size %zd, request 0x%p\n", __func__, size, req); > req->rl_connect_cookie = 0; /* our reserved value */ > rqst->rq_buffer = req->rl_sendbuf->rg_base; > + rqst->rq_rbuffer = (char *)rqst->rq_buffer + rqst->rq_rcvsize; > return 0; > > out_rdmabuf: > > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >