Re: [PATCH 5/9] SUNRPC: Initialize rpc_rqst outside of xprt->reserve_lock

[Anna Schumaker <Anna.Schumaker@Netapp.com>]

On 03/07/2018 03:23 PM, Chuck Lever wrote:
> 
> 
>> On Mar 7, 2018, at 3:00 PM, Anna Schumaker <Anna.Schumaker@netapp.com> wrote:
>>
>>
>>
>> On 03/06/2018 05:30 PM, Chuck Lever wrote:
>>>
>>>
>>>> On Mar 6, 2018, at 5:07 PM, Chuck Lever <chuck.lever@oracle.com> wrote:
>>>>
>>>>
>>>>
>>>>> On Mar 6, 2018, at 5:02 PM, Anna Schumaker <Anna.Schumaker@netapp.com> wrote:
>>>>>
>>>>> Hi Chuck,
>>>>>
>>>>> I'm seeing a huge performance hit with this patch.  I'm just running cthon over TCP, and it goes from finishing in 22 seconds to taking well over 5 minutes.  I seem to only see this on the read and write tests, such as basic test5 taking a minute to finish:
>>>>>
>>>>>  ./test5: read and write                                                                                       
>>>>>          wrote 1048576 byte file 10 times in 60.35 seconds (173737 bytes/sec)                                  
>>>>>          read 1048576 byte file 10 times in 0.0  seconds (-2147483648 bytes/sec)                               
>>>>>          ./test5 ok. 
>>>>
>>>> OK. This looks like write is impacted, but this test doesn't
>>>> actually perform any reads on the wire. Try iozone with -I,
>>>> maybe? That would show results for both read and write.
>>>
>>> Hum.
>>>
>>> Stock v4.16-rc4:
>>>
>>> ./test5: read and write
>>> 	wrote 1048576 byte file 10 times in 0.2  seconds (350811642 bytes/sec)
>>> 	read 1048576 byte file 10 times in 0.0  seconds (-2147483648 bytes/sec)
>>> 	./test5 ok.
>>>
>>>
>>> v4.16-rc4 with my full set of patches:
>>>
>>> ./test5: read and write
>>> 	wrote 1048576 byte file 10 times in 0.2  seconds (354236681 bytes/sec)
>>> 	read 1048576 byte file 10 times in 0.0  seconds (-2147483648 bytes/sec)
>>> 	./test5 ok.
>>>
>>> I don't see a regression here. Let me know how it goes!
>>
>> I'm using rc4 too, so maybe it's something different in my setup?
> 
> What is your setup, exactly? I assume your client is maybe a
> single CPU guest, and the server is the same, and both are
> hosted on one system?

Client is single CPU kvm guest with 1 gig ram, server is also kvm on the same system with 2 cpus and 4 gigs ram.

> 
> 
>> Making this change fixes the issue for me:
>>
>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>> index a394b4635f8e..273847f7e455 100644
>> --- a/net/sunrpc/xprt.c
>> +++ b/net/sunrpc/xprt.c
>> @@ -987,8 +987,6 @@ bool xprt_prepare_transmit(struct rpc_task *task)
>>                task->tk_status = -EAGAIN;
>>                goto out_unlock;
>>        }
>> -       if (likely(!bc_prealloc(req)))
>> -               req->rq_xid = xprt_alloc_xid(xprt);
>>        ret = true;
>> out_unlock:
>>        spin_unlock_bh(&xprt->transport_lock);
>> @@ -1315,6 +1313,7 @@ void xprt_request_init(struct rpc_task *task)
>>        req->rq_task    = task;
>>        req->rq_xprt    = xprt;
>>        req->rq_buffer  = NULL;
>> +       req->rq_xid     = xprt_alloc_xid(xprt);
> 
> xprt_alloc_xid is just 
> 
> 1299 static inline __be32 xprt_alloc_xid(struct rpc_xprt *xprt)
> 1300 {
> 1301         return (__force __be32)xprt->xid++;
> 1302 }
> 
> I don't believe the new call site for xprt_request_init is
> adequately serialized for this to be safe in general. That's why
> I'm calling xprt_alloc_xid in xprt_prepare_transmit, behind the
> transport_lock.

This makes sense.

> 
> However, I think we need to explain why that helps your performance
> issue, because it doesn't make sense to me that this would make a
> difference. Why did you think to try this change? Is there evidence
> on the wire of XID re-use, for example?

I selectively reverted parts of your original patch until I found the parts that kill my performance.

> 
> 
>>        req->rq_connect_cookie = xprt->connect_cookie - 1;
>>        req->rq_bytes_sent = 0;
>>        req->rq_snd_buf.len = 0;
>>
>>
>> Anna
>>
>>>
>>>
>>>>> I haven't dug into this too deeply, but my best guess is that maybe it's due to adding a call to xprt_request_init() in net/sunrpc/clnt.c:call_reserveresult()
>>>>
>>>> It wasn't added there, it was moved from xprt_alloc_slot. So,
>>>> it's not new work per-RPC.
>>>>
>>>> Any additional information would be appreciated!
>>>>
>>>>
>>>>> Thoughts?
>>>>> Anna
>>>>>
>>>>> On 03/05/2018 03:13 PM, Chuck Lever wrote:
>>>>>> alloc_slot is a transport-specific op, but initializing an rpc_rqst
>>>>>> is common to all transports. Move initialization to common code in
>>>>>> preparation for adding a transport-specific alloc_slot to xprtrdma.
>>>>>>
>>>>>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>>>>>> ---
>>>>>> include/linux/sunrpc/xprt.h |    1 +
>>>>>> net/sunrpc/clnt.c           |    1 +
>>>>>> net/sunrpc/xprt.c           |   12 +++++++-----
>>>>>> 3 files changed, 9 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
>>>>>> index 5fea0fb..9784e28 100644
>>>>>> --- a/include/linux/sunrpc/xprt.h
>>>>>> +++ b/include/linux/sunrpc/xprt.h
>>>>>> @@ -324,6 +324,7 @@ struct xprt_class {
>>>>>> struct rpc_xprt		*xprt_create_transport(struct xprt_create *args);
>>>>>> void			xprt_connect(struct rpc_task *task);
>>>>>> void			xprt_reserve(struct rpc_task *task);
>>>>>> +void			xprt_request_init(struct rpc_task *task);
>>>>>> void			xprt_retry_reserve(struct rpc_task *task);
>>>>>> int			xprt_reserve_xprt(struct rpc_xprt *xprt, struct rpc_task *task);
>>>>>> int			xprt_reserve_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task);
>>>>>> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
>>>>>> index 6e432ec..226f558 100644
>>>>>> --- a/net/sunrpc/clnt.c
>>>>>> +++ b/net/sunrpc/clnt.c
>>>>>> @@ -1546,6 +1546,7 @@ void rpc_force_rebind(struct rpc_clnt *clnt)
>>>>>> 	task->tk_status = 0;
>>>>>> 	if (status >= 0) {
>>>>>> 		if (task->tk_rqstp) {
>>>>>> +			xprt_request_init(task);
>>>>>> 			task->tk_action = call_refresh;
>>>>>> 			return;
>>>>>> 		}
>>>>>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>>>>>> index 70f0050..a394b46 100644
>>>>>> --- a/net/sunrpc/xprt.c
>>>>>> +++ b/net/sunrpc/xprt.c
>>>>>> @@ -66,7 +66,7 @@
>>>>>> * Local functions
>>>>>> */
>>>>>> static void	 xprt_init(struct rpc_xprt *xprt, struct net *net);
>>>>>> -static void	xprt_request_init(struct rpc_task *, struct rpc_xprt *);
>>>>>> +static __be32	xprt_alloc_xid(struct rpc_xprt *xprt);
>>>>>> static void	xprt_connect_status(struct rpc_task *task);
>>>>>> static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);
>>>>>> static void     __xprt_put_cong(struct rpc_xprt *, struct rpc_rqst *);
>>>>>> @@ -987,6 +987,8 @@ bool xprt_prepare_transmit(struct rpc_task *task)
>>>>>> 		task->tk_status = -EAGAIN;
>>>>>> 		goto out_unlock;
>>>>>> 	}
>>>>>> +	if (likely(!bc_prealloc(req)))
>>>>>> +		req->rq_xid = xprt_alloc_xid(xprt);
>>>>>> 	ret = true;
>>>>>> out_unlock:
>>>>>> 	spin_unlock_bh(&xprt->transport_lock);
>>>>>> @@ -1163,10 +1165,10 @@ void xprt_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task)
>>>>>> out_init_req:
>>>>>> 	xprt->stat.max_slots = max_t(unsigned int, xprt->stat.max_slots,
>>>>>> 				     xprt->num_reqs);
>>>>>> +	spin_unlock(&xprt->reserve_lock);
>>>>>> +
>>>>>> 	task->tk_status = 0;
>>>>>> 	task->tk_rqstp = req;
>>>>>> -	xprt_request_init(task, xprt);
>>>>>> -	spin_unlock(&xprt->reserve_lock);
>>>>>> }
>>>>>> EXPORT_SYMBOL_GPL(xprt_alloc_slot);
>>>>>>
>>>>>> @@ -1303,8 +1305,9 @@ static inline void xprt_init_xid(struct rpc_xprt *xprt)
>>>>>> 	xprt->xid = prandom_u32();
>>>>>> }
>>>>>>
>>>>>> -static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
>>>>>> +void xprt_request_init(struct rpc_task *task)
>>>>>> {
>>>>>> +	struct rpc_xprt *xprt = task->tk_xprt;
>>>>>> 	struct rpc_rqst	*req = task->tk_rqstp;
>>>>>>
>>>>>> 	INIT_LIST_HEAD(&req->rq_list);
>>>>>> @@ -1312,7 +1315,6 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
>>>>>> 	req->rq_task	= task;
>>>>>> 	req->rq_xprt    = xprt;
>>>>>> 	req->rq_buffer  = NULL;
>>>>>> -	req->rq_xid     = xprt_alloc_xid(xprt);
>>>>>> 	req->rq_connect_cookie = xprt->connect_cookie - 1;
>>>>>> 	req->rq_bytes_sent = 0;
>>>>>> 	req->rq_snd_buf.len = 0;
>>>>>>
>>>>
>>>> --
>>>> Chuck Lever
>>>>
>>>>
>>>>
>>>> --
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>>>
>>> --
>>> Chuck Lever
> 
> --
> Chuck Lever
> 
> 
>