Re: [PATCH v1 05/12] xprtrdma: Account for RPC/RDMA header size when deciding to inline

Chuck Lever
2015-07-12T17:52:15Z

Hi Sagi-

On Jul 12, 2015, at 10:37 AM, Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org> wrote:

> On 7/9/2015 11:42 PM, Chuck Lever wrote:
>> When marshaling RPC/RDMA requests, ensure the combined size of
>> RPC/RDMA header and RPC header do not exceed the inline threshold.
>> Endpoints typically reject RPC/RDMA messages that exceed the size
>> of their receive buffers.
>
> Did this solve a bug? because is seems like it does.
> Maybe it will be a good idea to describe this bug.

There’s no bugzilla for this, as no issue has been encountered
in the field so far. It’s hard to trigger and servers are
forgiving.

I added some text in the patch description.

>> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
>> ---
>> net/sunrpc/xprtrdma/rpc_rdma.c | 29 +++++++++++++++++++++++++++--
>> 1 file changed, 27 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
>> index 84ea37d..8cf9402 100644
>> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
>> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
>> @@ -71,6 +71,31 @@ static const char transfertypes[][12] = {
>> };
>> #endif
>>
>> +/* The client can send a request inline as long as the RPCRDMA header
>> + * plus the RPC call fit under the transport's inline limit. If the
>> + * combined call message size exceeds that limit, the client must use
>> + * the read chunk list for this operation.
>> + */
>> +static bool rpcrdma_args_inline(struct rpc_rqst *rqst)
>
> maybe static inline?

The final paragraph of Chapter 15 of Documentation/CodingStyle
suggests “static inline” is undesirable here. I think gcc makes
the correct inlining choice here by itself.

>> +{
>> + unsigned int callsize = RPCRDMA_HDRLEN_MIN + rqst->rq_snd_buf.len;
>> +
>> + return callsize <= RPCRDMA_INLINE_WRITE_THRESHOLD(rqst);
>> +}
>> +
>> +/* The client can’t know how large the actual reply will be. Thus it
>> + * plans for the largest possible reply for that particular ULP
>> + * operation. If the maximum combined reply message size exceeds that
>> + * limit, the client must provide a write list or a reply chunk for
>> + * this request.
>> + */
>> +static bool rpcrdma_results_inline(struct rpc_rqst *rqst)
>> +{
>> + unsigned int repsize = RPCRDMA_HDRLEN_MIN + rqst->rq_rcv_buf.buflen;
>> +
>> + return repsize <= RPCRDMA_INLINE_READ_THRESHOLD(rqst);
>> +}
>> +
>> /*
>> * Chunk assembly from upper layer xdr_buf.
>> *
>> @@ -418,7 +443,7 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
>> * a READ, then use write chunks to separate the file data
>> * into pages; otherwise use reply chunks.
>> */
>> - if (rqst->rq_rcv_buf.buflen <= RPCRDMA_INLINE_READ_THRESHOLD(rqst))
>> + if (rpcrdma_results_inline(rqst))
>> wtype = rpcrdma_noch;
>> else if (rqst->rq_rcv_buf.page_len == 0)
>> wtype = rpcrdma_replych;
>> @@ -441,7 +466,7 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
>> * implies the op is a write.
>> * TBD check NFSv4 setacl
>> */
>> - if (rqst->rq_snd_buf.len <= RPCRDMA_INLINE_WRITE_THRESHOLD(rqst))
>> + if (rpcrdma_args_inline(rqst))
>> rtype = rpcrdma_noch;
>> else if (rqst->rq_snd_buf.page_len == 0)
>> rtype = rpcrdma_areadch;
>>

--
Chuck Lever