[v2,05/22] SUNRPC: Separate buffer pointers for RPC Call and Reply messages
diff mbox

Message ID 20160823175244.13038.39619.stgit@manet.1015granger.net
State Under Review
Delegated to: Trond Myklebust
Headers show

Commit Message

Chuck Lever Aug. 23, 2016, 5:52 p.m. UTC
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(-)


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Comments

Schumaker, Anna Aug. 29, 2016, 2:23 p.m. UTC | #1
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.

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:
> 
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> 

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Chuck Lever Aug. 29, 2016, 3:33 p.m. UTC | #2
> 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
>> 
> 
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--
Chuck Lever



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Schumaker, Anna Aug. 29, 2016, 3:44 p.m. UTC | #3
On 08/29/2016 11:33 AM, Chuck Lever wrote:
> 
>> 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.

Got it.  The cacheline reason is good enough for me, so you don't need to change the patch.

Thanks,
Anna

> 
> 
>> 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
>>>
>>
>> --
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> 
> --
> Chuck Lever
> 
> 
> 

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Patch
diff mbox

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;
 	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: