From: Chuck Lever <chuck.lever@oracle.com>
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v3 26/44] SUNRPC: Improve latency for interactive tasks
Date: Wed, 2 Jan 2019 14:08:01 -0500 [thread overview]
Message-ID: <BDD7E434-DE5C-441C-8ED3-4A3CA28B7A36@oracle.com> (raw)
In-Reply-To: <3e3c803dd0d007e4692ae2142b73bc1294d2b62a.camel@hammerspace.com>
> On Jan 2, 2019, at 1:57 PM, Trond Myklebust <trondmy@hammerspace.com> wrote:
>
> On Wed, 2019-01-02 at 13:51 -0500, Chuck Lever wrote:
>>> On Jan 2, 2019, at 1:45 PM, Trond Myklebust <
>>> trondmy@hammerspace.com> wrote:
>>>
>>> On Wed, 2019-01-02 at 13:17 -0500, Chuck Lever wrote:
>>>>> On Dec 31, 2018, at 2:21 PM, Trond Myklebust <
>>>>> trondmy@hammerspace.com> wrote:
>>>>>
>>>>> On Mon, 2018-12-31 at 19:18 +0000, Trond Myklebust wrote:
>>>>>> On Mon, 2018-12-31 at 14:09 -0500, Chuck Lever wrote:
>>>>>>>> On Dec 31, 2018, at 1:59 PM, Trond Myklebust <
>>>>>>>> trondmy@hammerspace.com> wrote:
>>>>>>>>
>>>>>>>>
>>>>>> The test for rpcauth_xmit_need_reencode() happens when we
>>>>>> call
>>>>>> xprt_request_transmit() to actually put the RPC call on the
>>>>>> wire.
>>>>>> The
>>>>>> enqueue order should not be able to defeat that test.
>>>>>>
>>>>>> Hmm... Is it perhaps the test for req->rq_bytes_sent that is
>>>>>> failing
>>>>>> because this is a retransmission after a disconnect/reconnect
>>>>>> that
>>>>>> didn't trigger a re-encode?
>>>>>
>>>>> Actually, it might be worth a try to move the test for
>>>>> rpcauth_xmit_need_reencode() outside the enclosing test for
>>>>> req-
>>>>>> rq_bytes_sent as that is just a minor optimisation.
>>>>
>>>> Perhaps that's the case for TCP, but RPCs sent via xprtrdma never
>>>> set
>>>> req->rq_bytes_sent to a non-zero value. The body of the "if"
>>>> statement
>>>> is always executed for those RPCs.
>>>>
>>>
>>> Then the question is what is defeating the call to
>>> rpcauth_xmit_need_reencode() in xprt_request_transmit() and causing
>>> it
>>> not to trigger in the misordered cases?
>>
>> Here's a sample RPC/RDMA case.
>>
>> My instrumented server reports this:
>>
>> Jan 2 13:29:00 klimt kernel: gss_check_seq_num: dropped:
>> seq_num=141220 sd->sd_max=141360
>>
>>
>> ftrace log on the client shows this:
>>
>> kworker/u28:12-2191 [004] 194.048534: rpcgss_need_reencode:
>> task:1761@5 xid=0x88f4f47c rq_seqno=141220 seq_xmit=141336 reencode
>> unneeded
>> kworker/u28:12-2191 [004] 194.048534:
>> xprt_transmit: task:1761@5 xid=0x88f4f47c seqno=141220
>> status=-57
>> kworker/u28:12-2191 [004] 194.048534:
>> rpc_task_run_action: task:1779@5 flags=ASYNC
>> runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=-57
>> action=call_transmit_status
>> kworker/u28:12-2191 [004] 194.048535:
>> rpc_task_run_action: task:1779@5 flags=ASYNC
>> runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=0
>> action=call_transmit
>> kworker/u28:12-2191 [004] 194.048535:
>> rpc_task_sleep: task:1779@5 flags=ASYNC
>> runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=-11 timeout=0
>> queue=xprt_sending
>>
>>
>> kworker/u28:12-2191 [004] 194.048552: rpcgss_need_reencode:
>> task:1761@5 xid=0x88f4f47c rq_seqno=141220 seq_xmit=141336 reencode
>> unneeded
>> kworker/u28:12-2191 [004] 194.048557:
>> xprt_transmit: task:1761@5 xid=0x88f4f47c seqno=141220
>> status=0
>>
>>
>> kworker/u28:12-2191 [004] 194.048559: rpcgss_need_reencode:
>> task:1902@5 xid=0x14f5f47c rq_seqno=141360 seq_xmit=141336 reencode
>> unneeded
>> kworker/u28:12-2191 [004] 194.048563:
>> xprt_transmit: task:1902@5 xid=0x14f5f47c seqno=141360
>> status=0
>>
>>
>> Note that first need_reencode: the sequence numbers show that the
>> xmit
>> queue has been significantly re-ordered. The request being
>> transmitted is
>> already very close to the lower end of the GSS sequence number
>> window.
>>
>> The server then re-ordereds these two slightly because the first one
>> had
>> some Read chunks that need to be pulled over, the second was pure
>> inline
>> and therefore could be processed immediately. That is enough to force
>> the
>> first one outside the GSS sequence number window.
>>
>> I haven't looked closely at the pathology of the TCP case.
>
> Wait a minute... That's not OK. The client can't be expected to take
> into account reordering that happens on the server side.
Conversely, the client can't assume the transport and the server don't
re-order. This does not appear to be a problem for the v4.19 client:
I don't see disconnect storms with that client.
--
Chuck Lever
next prev parent reply other threads:[~2019-01-02 19:08 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-17 13:02 [PATCH v3 00/44] Convert RPC client transmission to a queued model Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 01/44] SUNRPC: Clean up initialisation of the struct rpc_rqst Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 02/44] SUNRPC: If there is no reply expected, bail early from call_decode Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 03/44] SUNRPC: The transmitted message must lie in the RPCSEC window of validity Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 04/44] SUNRPC: Simplify identification of when the message send/receive is complete Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 05/44] SUNRPC: Avoid holding locks across the XDR encoding of the RPC message Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 06/44] SUNRPC: Rename TCP receive-specific state variables Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 07/44] SUNRPC: Move reset of TCP state variables into the reconnect code Trond Myklebust
2018-09-17 13:02 ` [PATCH v3 08/44] SUNRPC: Add socket transmit queue offset tracking Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 09/44] SUNRPC: Simplify dealing with aborted partially transmitted messages Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 10/44] SUNRPC: Refactor the transport request pinning Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 11/44] SUNRPC: Add a helper to wake up a sleeping rpc_task and set its status Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 12/44] SUNRPC: Test whether the task is queued before grabbing the queue spinlocks Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 13/44] SUNRPC: Don't wake queued RPC calls multiple times in xprt_transmit Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 14/44] SUNRPC: Rename xprt->recv_lock to xprt->queue_lock Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 15/44] SUNRPC: Refactor xprt_transmit() to remove the reply queue code Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 16/44] SUNRPC: Refactor xprt_transmit() to remove wait for reply code Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 17/44] SUNRPC: Minor cleanup for call_transmit() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 18/44] SUNRPC: Distinguish between the slot allocation list and receive queue Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 19/44] SUNRPC: Add a transmission queue for RPC requests Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 20/44] SUNRPC: Refactor RPC call encoding Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 21/44] SUNRPC: Fix up the back channel transmit Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 22/44] SUNRPC: Treat the task and request as separate in the xprt_ops->send_request() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 23/44] SUNRPC: Don't reset the request 'bytes_sent' counter when releasing XPRT_LOCK Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 24/44] SUNRPC: Simplify xprt_prepare_transmit() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 25/44] SUNRPC: Move RPC retransmission stat counter to xprt_transmit() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 26/44] SUNRPC: Improve latency for interactive tasks Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 27/44] SUNRPC: Support for congestion control when queuing is enabled Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 28/44] SUNRPC: Enqueue swapper tagged RPCs at the head of the transmit queue Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 29/44] SUNRPC: Allow calls to xprt_transmit() to drain the entire " Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 30/44] SUNRPC: Allow soft RPC calls to time out when waiting for the XPRT_LOCK Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 31/44] SUNRPC: Turn off throttling of RPC slots for TCP sockets Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 32/44] SUNRPC: Clean up transport write space handling Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 33/44] SUNRPC: Cleanup: remove the unused 'task' argument from the request_send() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 34/44] SUNRPC: Don't take transport->lock unnecessarily when taking XPRT_LOCK Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 35/44] SUNRPC: Convert xprt receive queue to use an rbtree Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 36/44] SUNRPC: Fix priority queue fairness Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 37/44] SUNRPC: Convert the xprt->sending queue back to an ordinary wait queue Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 38/44] SUNRPC: Add a label for RPC calls that require allocation on receive Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 39/44] SUNRPC: Add a bvec array to struct xdr_buf for use with iovec_iter() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 40/44] SUNRPC: Simplify TCP receive code by switching to using iterators Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 41/44] SUNRPC: Clean up - rename xs_tcp_data_receive() to xs_stream_data_receive() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 42/44] SUNRPC: Allow AF_LOCAL sockets to use the generic stream receive Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 43/44] SUNRPC: Clean up xs_udp_data_receive() Trond Myklebust
2018-09-17 13:03 ` [PATCH v3 44/44] SUNRPC: Unexport xdr_partial_copy_from_skb() Trond Myklebust
2018-09-17 20:44 ` [PATCH v3 40/44] SUNRPC: Simplify TCP receive code by switching to using iterators Trond Myklebust
2018-11-09 11:19 ` Catalin Marinas
2018-11-29 19:28 ` Cristian Marussi
2018-11-29 19:56 ` Trond Myklebust
2018-11-30 16:19 ` Cristian Marussi
2018-11-30 19:31 ` Trond Myklebust
2018-12-02 16:44 ` Trond Myklebust
2018-12-03 11:45 ` Catalin Marinas
2018-12-03 11:53 ` Cristian Marussi
2018-12-03 18:54 ` Cristian Marussi
2018-12-27 19:21 ` [PATCH v3 26/44] SUNRPC: Improve latency for interactive tasks Chuck Lever
2018-12-27 22:14 ` Trond Myklebust
2018-12-27 22:34 ` Chuck Lever
2018-12-31 18:09 ` Trond Myklebust
2018-12-31 18:44 ` Chuck Lever
2018-12-31 18:59 ` Trond Myklebust
2018-12-31 19:09 ` Chuck Lever
2018-12-31 19:18 ` Trond Myklebust
2018-12-31 19:21 ` Trond Myklebust
2019-01-02 18:17 ` Chuck Lever
2019-01-02 18:45 ` Trond Myklebust
2019-01-02 18:51 ` Chuck Lever
2019-01-02 18:57 ` Trond Myklebust
2019-01-02 19:06 ` Trond Myklebust
2019-01-02 19:24 ` Trond Myklebust
2019-01-02 19:33 ` Chuck Lever
2019-01-02 19:08 ` Chuck Lever [this message]
2019-01-02 19:11 ` Trond Myklebust
2018-09-18 21:01 ` [PATCH v3 15/44] SUNRPC: Refactor xprt_transmit() to remove the reply queue code Anna Schumaker
2018-09-19 15:48 ` Trond Myklebust
2018-09-19 17:30 ` Anna Schumaker
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