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From: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
To: Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>
Cc: List Linux RDMA Mailing
	<linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Linux NFS Mailing List
	<linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH v2 05/22] SUNRPC: Separate buffer pointers for RPC Call and Reply messages
Date: Mon, 29 Aug 2016 11:33:41 -0400	[thread overview]
Message-ID: <10EFE631-06F6-4E4E-9EBC-F7ABFDF2C742@oracle.com> (raw)
In-Reply-To: <1e9440d8-111a-4252-c706-2e3c26f7b09a-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>


> On Aug 29, 2016, at 10:23 AM, Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org> wrote:
> 
> 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 <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
>> ---
>> 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.

Hi Anna-

Keeping related fields together is usually more important than an extra
line or two in a commit. At the very least, the function of these fields
is more clear (to me, anyway) in this order.

Generally it's good practice to keep together structure fields that are
used at the same time. These four fields might appear in the same CPU
cacheline, though that can change as fields are introduced or removed
earlier in struct rpc_rqst.

An argument can be made that the code is just as easy to read this way:

        void                    *rq_buffer, *rq_rbuffer;
        size_t                  rq_callsize, rq_rcvsize;

If that's your preference as maintainer, I will change it in the next
version of this series.


> 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
Chuck Lever



--
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WARNING: multiple messages have this Message-ID
From: Chuck Lever <chuck.lever@oracle.com>
To: Anna Schumaker <Anna.Schumaker@netapp.com>
Cc: List Linux RDMA Mailing <linux-rdma@vger.kernel.org>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v2 05/22] SUNRPC: Separate buffer pointers for RPC Call and Reply messages
Date: Mon, 29 Aug 2016 11:33:41 -0400	[thread overview]
Message-ID: <10EFE631-06F6-4E4E-9EBC-F7ABFDF2C742@oracle.com> (raw)
In-Reply-To: <1e9440d8-111a-4252-c706-2e3c26f7b09a@Netapp.com>


> On Aug 29, 2016, at 10:23 AM, Anna Schumaker <Anna.Schumaker@netapp.com> wrote:
> 
> 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 <chuck.lever@oracle.com>
>> ---
>> 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.

Hi Anna-

Keeping related fields together is usually more important than an extra
line or two in a commit. At the very least, the function of these fields
is more clear (to me, anyway) in this order.

Generally it's good practice to keep together structure fields that are
used at the same time. These four fields might appear in the same CPU
cacheline, though that can change as fields are introduced or removed
earlier in struct rpc_rqst.

An argument can be made that the code is just as easy to read this way:

        void                    *rq_buffer, *rq_rbuffer;
        size_t                  rq_callsize, rq_rcvsize;

If that's your preference as maintainer, I will change it in the next
version of this series.


> 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
>> 
> 
> --
> 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

--
Chuck Lever




  parent reply	other threads:[~2016-08-29 15:33 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-23 17:52 [PATCH v2 00/22] client-side NFS/RDMA patches proposed for v4.9 Chuck Lever
2016-08-23 17:52 ` Chuck Lever
     [not found] ` <20160823174402.13038.84561.stgit-FYjufvaPoItvLzlybtyyYzGyq/o6K9yX@public.gmane.org>
2016-08-23 17:52   ` [PATCH v2 01/22] xprtrdma: Eliminate INLINE_THRESHOLD macros Chuck Lever
2016-08-23 17:52     ` Chuck Lever
2016-08-23 17:52   ` [PATCH v2 02/22] SUNRPC: Refactor rpc_xdr_buf_init() Chuck Lever
2016-08-23 17:52     ` Chuck Lever
     [not found]     ` <20160823175219.13038.22735.stgit-FYjufvaPoItvLzlybtyyYzGyq/o6K9yX@public.gmane.org>
2016-08-26 21:05       ` Anna Schumaker
2016-08-26 21:05         ` Anna Schumaker
2016-08-23 17:52   ` [PATCH v2 03/22] SUNRPC: Generalize the RPC buffer allocation API Chuck Lever
2016-08-23 17:52     ` Chuck Lever
2016-08-23 17:52   ` [PATCH v2 04/22] SUNRPC: Generalize the RPC buffer release API Chuck Lever
2016-08-23 17:52     ` Chuck Lever
2016-08-23 17:52   ` [PATCH v2 05/22] SUNRPC: Separate buffer pointers for RPC Call and Reply messages Chuck Lever
2016-08-23 17:52     ` Chuck Lever
     [not found]     ` <20160823175244.13038.39619.stgit-FYjufvaPoItvLzlybtyyYzGyq/o6K9yX@public.gmane.org>
2016-08-29 14:23       ` Anna Schumaker
2016-08-29 14:23         ` Anna Schumaker
     [not found]         ` <1e9440d8-111a-4252-c706-2e3c26f7b09a-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2016-08-29 15:33           ` Chuck Lever [this message]
2016-08-29 15:33             ` Chuck Lever
     [not found]             ` <10EFE631-06F6-4E4E-9EBC-F7ABFDF2C742-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2016-08-29 15:44               ` Anna Schumaker
2016-08-29 15:44                 ` Anna Schumaker
2016-08-23 17:52   ` [PATCH v2 06/22] SUNRPC: Add a transport-specific private field in rpc_rqst Chuck Lever
2016-08-23 17:52     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 07/22] xprtrdma: Initialize separate RPC call and reply buffers Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 08/22] xprtrdma: Use smaller buffers for RPC-over-RDMA headers Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 09/22] xprtrdma: Replace DMA_BIDIRECTIONAL Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 10/22] xprtrdma: Delay DMA mapping Send and Receive buffers Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 11/22] xprtrdma: Eliminate "ia" argument in rpcrdma_{alloc, free}_regbuf Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 12/22] xprtrdma: Simplify rpcrdma_ep_post_recv() Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 13/22] xprtrdma: Move send_wr to struct rpcrdma_req Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:53   ` [PATCH v2 14/22] xprtrdma: Move recv_wr to struct rpcrdma_rep Chuck Lever
2016-08-23 17:53     ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 15/22] rpcrdma: RDMA/CM private message data structure Chuck Lever
2016-08-23 17:54     ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 16/22] xprtrdma: Client-side support for rpcrdma_connect_private Chuck Lever
2016-08-23 17:54     ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 17/22] xprtrdma: Basic support for Remote Invalidation Chuck Lever
2016-08-23 17:54     ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 18/22] xprtrdma: Use gathered Send for large inline messages Chuck Lever
2016-08-23 17:54     ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 19/22] xprtrdma: Support larger inline thresholds Chuck Lever
2016-08-23 17:54     ` Chuck Lever
     [not found]     ` <20160823175438.13038.1624.stgit-FYjufvaPoItvLzlybtyyYzGyq/o6K9yX@public.gmane.org>
2016-08-29 19:52       ` Anna Schumaker
2016-08-29 19:52         ` Anna Schumaker
     [not found]         ` <c922120b-35f3-65bf-e778-3cef645cee48-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2016-08-29 20:02           ` Chuck Lever
2016-08-29 20:02             ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 20/22] xprtrmda: Report address of frmr, not mw Chuck Lever
2016-08-23 17:54     ` Chuck Lever
     [not found]     ` <20160823175446.13038.58792.stgit-FYjufvaPoItvLzlybtyyYzGyq/o6K9yX@public.gmane.org>
2016-08-29 19:54       ` Anna Schumaker
2016-08-29 19:54         ` Anna Schumaker
     [not found]         ` <7f92664a-a16c-6c44-b8f8-391e4fec0a89-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2016-08-29 20:13           ` Chuck Lever
2016-08-29 20:13             ` Chuck Lever
2016-08-23 17:54   ` [PATCH v2 21/22] xprtrdma: Rename rpcrdma_receive_wc() Chuck Lever
2016-08-23 17:54     ` Chuck Lever
2016-08-23 17:55   ` [PATCH v2 22/22] xprtrdma: Eliminate rpcrdma_receive_worker() Chuck Lever
2016-08-23 17:55     ` Chuck Lever

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