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

Chuck Lever
2015-07-10T19:33:55Z

On Jul 10, 2015, at 3:21 PM, Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org> 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-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
>> ---
>> 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