On Nov 15, 2013, at 19:29, Tom Talpey <tom@xxxxxxxxxx> wrote:
> On 11/15/2013 5:53 PM, Myklebust, Trond wrote:
>>
>> On Nov 15, 2013, at 17:31, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>
>>>
>>> On Nov 15, 2013, at 5:29 PM, "Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> wrote:
>>>
>>>>
>>>> On Nov 15, 2013, at 16:39, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>>
>>>>> Hi Trond-
>>>>>
>>>>> Klemens Senn <klemens.senn@xxxxxxxxx> says:
>>>>>> Hi,
>>>>>>
>>>>>> I started setting up NFS over RDMA on a OpenSUSE 12.3 machine using the
>>>>>> 3.7.10-1.16-default kernel.
>>>>>> Mounting the NFS share works and getting a file with 812 Bytes succeeds.
>>>>>> Reading 813 Bytes raises a Input/output error.
>>>>>>
>>>>>> The export on the server side is done with
>>>>>> /data
>>>>>> 172.16.100.0/24(rw,wdelay,crossmnt,insecure,no_root_squash,no_subtree_check,fsid=0,mountpoint)
>>>>>>
>>>>>> Following command is used for mounting the NFSv4 share:
>>>>>> mount -t nfs -o port=20049,rdma,vers=4.0,timeo=900 172.16.100.2:/ /mnt/
>>>>>>
>>>>>> Testing the client side with older kernels stated that the mount is
>>>>>> working properly with the 3.4.67 kernel. I continued testing with the
>>>>>> 3.10.17 kernel and enabled the debug level and noticed the message
>>>>>> "server cheating in read reply: count 813 > recvd 0"
>>>>>>
>>>>>> Here is the syslog output:
>>>>>> NFS: read(//813_bytes, 262144@0)
>>>>>> NFS: nfs_readpage (ffffea001db1e898 4096@0)
>>>>>> NFS: 0 initiated read call (req 0:33/70, 813 bytes @ offset 0)
>>>>>> RPC: new task initialized, procpid 9881
>>>>>> RPC: allocated task ffff88105dacabf8
>>>>>> RPC: 1631 __rpc_execute flags=0x1
>>>>>> <-- nfs4_setup_sequence status=0
>>>>>> RPC: 1631 call_start nfs4 proc READ (async)
>>>>>> RPC: 1631 call_reserve (status 0)
>>>>>> RPC: 1631 reserved req ffff88085e641c00 xid 3f6a89a6
>>>>>> RPC: 1631 call_reserveresult (status 0)
>>>>>> RPC: 1631 call_refresh (status 0)
>>>>>> RPC: 1631 refreshing UNIX cred ffff88087c2108c0
>>>>>> RPC: 1631 call_refreshresult (status 0)
>>>>>> RPC: 1631 call_allocate (status 0)
>>>>>> RPC: xprt_rdma_allocate: size 684, request 0xffff88084a342000
>>>>>> RPC: 1631 call_bind (status 0)
>>>>>> RPC: 1631 call_connect xprt ffff88085f297000 is connected
>>>>>> RPC: 1631 call_transmit (status 0)
>>>>>> RPC: 1631 xprt_prepare_transmit
>>>>>> RPC: 1631 xprt_cwnd_limited cong = 0 cwnd = 4096
>>>>>> RPC: 1631 rpc_xdr_encode (status 0)
>>>>>> RPC: 1631 marshaling UNIX cred ffff88087c2108c0
>>>>>> RPC: 1631 using AUTH_UNIX cred ffff88087c2108c0 to wrap rpc data
>>>>>> RPC: 1631 xprt_transmit(144)
>>>>>> RPC: rpcrdma_inline_pullup: pad 0 destp 0xffff88084a3437f0 len 144
>>>>>> hdrlen 144
>>>>>> RPC: rpcrdma_register_frmr_external: Using frmr ffff88084b612d10
>>>>>> to map 1 segments
>>>>>> RPC: rpcrdma_create_chunks: write chunk elem
>>>>>> 813@0x87bf95000:0x8a905 (more)
>>>>>> RPC: rpcrdma_register_frmr_external: Using frmr ffff88084b612d38
>>>>>> to map 1 segments
>>>>>> RPC: rpcrdma_create_chunks: write chunk elem
>>>>>> 152@0x84a343974:0x8aa01 (last)
>>>>>> RPC: rpcrdma_marshal_req: write chunk: hdrlen 68 rpclen 144 padlen
>>>>>> 0 headerp 0xffff88084a343100 base 0xffff88084a343760 lkey 0x8000
>>>>>> RPC: rpcrdma_event_process: event rep ffff88084b612d10 status 0
>>>>>> opcode 8 length 4294936584
>>>>>> RPC: rpcrdma_event_process: event rep ffff88084b612d38 status 0
>>>>>> opcode 8 length 4294936584
>>>>>> RPC: 1631 xmit complete
>>>>>> RPC: 1631 sleep_on(queue "xprt_pending" time 4296115067)
>>>>>> RPC: 1631 added to queue ffff88085f297258 "xprt_pending"
>>>>>> RPC: 1631 setting alarm for 90000 ms
>>>>>> RPC: wake_up_first(ffff88085f297190 "xprt_sending")
>>>>>> RPC: rpcrdma_event_process: event rep ffff88085e8bf000 status 0
>>>>>> opcode 80 length 128
>>>>>> RPC: rpcrdma_reply_handler: reply 0xffff88085e8bf000 completes
>>>>>> request 0xffff88084a342000
>>>>>> RPC request 0xffff88085e641c00 xid 0xa6896a3f
>>>>>> RPC: rpcrdma_count_chunks: chunk 813@0x87bf95000:0x8a905
>>>>>> RPC: rpcrdma_count_chunks: chunk 3@0x84a343974:0x8aa01
>>>>>> RPC: rpcrdma_inline_fixup: srcp 0xffff88085e8bf0a4 len 60 hdrlen 60
>>>>>> RPC: rpcrdma_reply_handler: xprt_complete_rqst(0xffff88085f297000,
>>>>>> 0xffff88085e641c00, 876)
>>>>>> RPC: 1631 xid 3f6a89a6 complete (876 bytes received)
>>>>>> RPC: 1631 __rpc_wake_up_task (now 4296115067)
>>>>>> RPC: 1631 disabling timer
>>>>>> RPC: 1631 removed from queue ffff88085f297258 "xprt_pending"
>>>>>> RPC: __rpc_wake_up_task done
>>>>>> RPC: 1631 __rpc_execute flags=0x801
>>>>>> RPC: 1631 call_status (status 876)
>>>>>> RPC: 1631 call_decode (status 876)
>>>>>> RPC: 1631 validating UNIX cred ffff88087c2108c0
>>>>>> RPC: 1631 using AUTH_UNIX cred ffff88087c2108c0 to unwrap rpc data
>>>>>> NFS: server cheating in read reply: count 813 > recvd 0
>>>>>> RPC: 1631 call_decode result 0
>>>>>> NFS: nfs_readpage_result: 1631, (status 0)
>>>>>> --> nfs4_read_done
>>>>>>
>>>>>> Adding other debug prints to the kernel module told me that
>>>>>> buf->page_len is set to 0 in xdr_align_pages (in file net/sunrpc/xdr.c).
>>>>>> Comparing this piece of code with older kernel versions showed that the
>>>>>> comparison with buf->page_len was introduces in kernel 3.7.
>>>>>> By disabling this check the file transfer seems to work.
>>>>>>
>>>>>> Here is the patch for kernel 3.10.17:
>>>>>>
>>>>>> --- net/sunrpc/xdr.c 2013-10-18 19:44:19.000000000 +0200
>>>>>> +++ net/sunrpc/xdr_new.c 2013-11-08 14:06:00.241217773 +0100
>>>>>> @@ -747,7 +747,7 @@
>>>>>> nwords = xdr->nwords;
>>>>>> len = nwords << 2;
>>>>>> }
>>>>>> - if (buf->page_len <= len)
>>>>>> + if (buf->page_len && buf->page_len <= len)
>>>>>> len = buf->page_len;
>>>>>> else if (nwords < xdr->nwords) {
>>>>>> /* Truncate page data and move it into the tail */
>>>>>>
>>>>>>
>>>>>> Can you please tell me which entity sets (or does not set) the total
>>>>>> length (buf->page_len) after receiving the data from the RDMA_SEND
>>>>>> operation from the server?
>>>>>>
>>>>>> Please advise
>>>>>>
>>>>>> Klemens
>>>>>
>>>>> Comparing xdr_align_pages() before commit a11a2bf4 and afterwords, it appears that it no longer handles cases where buf->page_len == 0 the same way it used to. xdr_align_pages() would never return zero unless xdr->nwords was zero.
>>>>
>>>> Why would the buf->page_len == 0 in a READ call? Has RDMA been relying on some kind of undocumented behaviour?
>>>
>>> See rpcrdma_inline_fixup().
>>
>> I see it, but I don’t get it. What is it trying to do?
>>
>> Firstly, why is it playing with rqst->rq_rcv_buf instead of using rq_private_buf? Secondly, why is it mucking with the page buffer length?
>>
>
> Speaking from memory, that routine was there originally to deliver
> the RDMA data into the iov list expected by the upper layer via
> RPC. When receiving via TCP, there were data copies that put it
> into the receive buffers, and the code tried to avoid a similar
> data copy - which would negate a big benefit of RDMA.
>
> That code was first written for the 2.4 kernel, and it appears to
> be working correctly today, except for the assertion stopping it.
> Has rq_private_buf been there since then?
Hi Tom,
I had to go back to the 'old-2.6-bkcvs’ repository in order to find the commit that introduced rq_private_buf. As far as I can tell, it debuted in the Linux 2.6.0-test4 kernel, which was released on August 22, 2003. That definitely predates the RDMA code, which was merged in September 2007.
Cheers
Trond--
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