Re: [PATCH v1 02/12] xprtrdma: Raise maximum payload size to one megabyte

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On Jul 10, 2015, at 3:21 PM, Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> wrote:

> Hi Chuck,
> 
> On 07/09/2015 04:41 PM, Chuck Lever wrote:
>> The point of larger rsize and wsize is to reduce the per-byte cost
>> of memory registration and deregistration. Modern HCAs can typically
>> handle a megabyte or more with a single registration operation.
>> 
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> net/sunrpc/xprtrdma/xprt_rdma.h |    3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>> 
>> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
>> index f49dd8b..abee472 100644
>> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
>> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
>> @@ -165,8 +165,7 @@ rdmab_to_msg(struct rpcrdma_regbuf *rb)
>>  * struct rpcrdma_buffer. N is the max number of outstanding requests.
>>  */
>> 
>> -/* temporary static scatter/gather max */
>> -#define RPCRDMA_MAX_DATA_SEGS	(64)	/* max scatter/gather */
>> +#define RPCRDMA_MAX_DATA_SEGS	((1 * 1024 * 1024) / PAGE_SIZE)
>                                         ^^^
> What is the significance of the 1 here?

This echoes the definition of RPCSVC_MAXPAYLOAD.

“1” documents “one” megabyte, I assume.


> Thanks,
> Anna
> 
>> #define RPCRDMA_MAX_SEGS 	(RPCRDMA_MAX_DATA_SEGS + 2) /* head+tail = 2 */
>> 
>> struct rpcrdma_buffer;
>> 
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> 
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--
Chuck Lever



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