Re: [PATCH] SUNRPC: Remove rpc_xprt::tsh_size

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] SUNRPC: Remove rpc_xprt::tsh_size
Date: Fri, 4 Jan 2019 16:35:23 -0500	[thread overview]
Message-ID: <EE4DED67-E4A7-4F82-A5D0-9137381A2B4A@oracle.com> (raw)
In-Reply-To: <1d6779ff05f2d31c4eccd048acbb28563bc9b79b.camel@hammerspace.com>

> On Jan 3, 2019, at 11:00 PM, Trond Myklebust <trondmy@hammerspace.com> wrote:
> 
> On Thu, 2019-01-03 at 17:49 -0500, Chuck Lever wrote:
>>> On Jan 3, 2019, at 4:35 PM, Chuck Lever <chuck.lever@oracle.com>
>>> wrote:
>>> 
>>>> On Jan 3, 2019, at 4:28 PM, Trond Myklebust <
>>>> trondmy@hammerspace.com> wrote:
>>>> 
>>>> On Thu, 2019-01-03 at 16:07 -0500, Chuck Lever wrote:
>>>>>> On Jan 3, 2019, at 3:53 PM, Chuck Lever <
>>>>>> chuck.lever@oracle.com>
>>>>>> wrote:
>>>>>> 
>>>>>>> On Jan 3, 2019, at 1:47 PM, Trond Myklebust <
>>>>>>> trondmy@hammerspace.com> wrote:
>>>>>>> 
>>>>>>> On Thu, 2019-01-03 at 13:29 -0500, Chuck Lever wrote:
>>>>>>>> +	reclen = req->rq_snd_buf.len;
>>>>>>>> +	marker = cpu_to_be32(RPC_LAST_STREAM_FRAGMENT |
>>>>>>>> reclen);
>>>>>>>> +	return kernel_sendmsg(transport->sock, &msg, &iov, 1,
>>>>>>>> iov.iov_len);
>>>>>>> 
>>>>>>> So what does this do for performance? I'd expect that
>>>>>>> adding
>>>>>>> another
>>>>>>> dive into the socket layer will come with penalties.
>>>>>> 
>>>>>> NFSv3 on TCP, sec=sys, 56Gbs IBoIP, v4.20 + my v4.21 patches
>>>>>> fio, 8KB random, 70% read, 30% write, 16 threads, iodepth=16
>>>>>> 
>>>>>> Without this patch:
>>>>>> 
>>>>>> read: IOPS=28.7k, BW=224MiB/s (235MB/s)(11.2GiB/51092msec)
>>>>>> write: IOPS=12.3k, BW=96.3MiB/s (101MB/s)(4918MiB/51092msec)
>>>>>> 
>>>>>> With this patch:
>>>>>> 
>>>>>> read: IOPS=28.6k, BW=224MiB/s (235MB/s)(11.2GiB/51276msec)
>>>>>> write: IOPS=12.3k, BW=95.8MiB/s (100MB/s)(4914MiB/51276msec)
>>>>>> 
>>>>>> Seems like that's in the noise.
>>>>> 
>>>>> Sigh. That's because it was the same kernel. Again, with
>>>>> feeling:
>>>>> 
>>>>> 4.20.0-rc7-00048-g9274254:
>>>>> read: IOPS=28.6k, BW=224MiB/s (235MB/s)(11.2GiB/51276msec)
>>>>> write: IOPS=12.3k, BW=95.8MiB/s (100MB/s)(4914MiB/51276msec)
>>>>> 
>>>>> 4.20.0-rc7-00049-ga4dea15:
>>>>> read: IOPS=27.2k, BW=212MiB/s (223MB/s)(11.2GiB/53979msec)
>>>>> write: IOPS=11.7k, BW=91.1MiB/s (95.5MB/s)(4917MiB/53979msec)
>>>>> 
>>>> 
>>>> So about a 5% reduction in performance?
>>> 
>>> On this workload, yes.
>>> 
>>> Could send the record marker in xs_send_kvec with the head[0]
>>> iovec.
>>> I'm going to try that next.
>> 
>> That helps:
>> 
>> Linux 4.20.0-rc7-00049-g664f679 #651 SMP Thu Jan 3 17:35:26 EST 2019
>> 
>>   read: IOPS=28.7k, BW=224MiB/s (235MB/s)(11.2GiB/51185msec)
>>  write: IOPS=12.3k, BW=96.1MiB/s (101MB/s)(4919MiB/51185msec)
>> 
> 
> Interesting... Perhaps we might be able to eke out a few more percent
> performance on file writes by also converting xs_send_pagedata() to use
> a single sock_sendmsg() w/ iov_iter rather than looping through several
> calls to sendpage()?

IMO...

For small requests (say, smaller than 17 pages), packing the head, pagevec,
and tail into an iov_iter and sending them all via a single sock_sendmsg
call would likely be efficient.

For larger requests, other overheads would dominate. And you'd have
to keep around an iter array that held 257 entries... You could pass a
large pagevec to sock_sendmsg in smaller chunks.

Are you thinking of converting xs_sendpages (or even xdr_bufs) to use
iov_iter directly?

--
Chuck Lever