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Subject: Re: [PATCH] SUNRPC: Remove rpc_xprt::tsh_size
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <1d6779ff05f2d31c4eccd048acbb28563bc9b79b.camel@hammerspace.com>
Date:   Fri, 4 Jan 2019 16:35:23 -0500
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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Message-Id: <EE4DED67-E4A7-4F82-A5D0-9137381A2B4A@oracle.com>
References: <20190103182649.4148.19838.stgit@manet.1015granger.net>
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 <076cce85045dbaab3ca40947b2599f96cff66b53.camel@hammerspace.com>
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To:     Trond Myklebust <trondmy@hammerspace.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Jan 3, 2019, at 11:00 PM, Trond Myklebust <trondmy@hammerspace.com> =
wrote:
>=20
> 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:
>>>=20
>>>> On Jan 3, 2019, at 4:28 PM, Trond Myklebust <
>>>> trondmy@hammerspace.com> wrote:
>>>>=20
>>>> 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:
>>>>>>=20
>>>>>>> On Jan 3, 2019, at 1:47 PM, Trond Myklebust <
>>>>>>> trondmy@hammerspace.com> wrote:
>>>>>>>=20
>>>>>>> On Thu, 2019-01-03 at 13:29 -0500, Chuck Lever wrote:
>>>>>>>> +	reclen =3D req->rq_snd_buf.len;
>>>>>>>> +	marker =3D cpu_to_be32(RPC_LAST_STREAM_FRAGMENT |
>>>>>>>> reclen);
>>>>>>>> +	return kernel_sendmsg(transport->sock, &msg, &iov, 1,
>>>>>>>> iov.iov_len);
>>>>>>>=20
>>>>>>> So what does this do for performance? I'd expect that
>>>>>>> adding
>>>>>>> another
>>>>>>> dive into the socket layer will come with penalties.
>>>>>>=20
>>>>>> NFSv3 on TCP, sec=3Dsys, 56Gbs IBoIP, v4.20 + my v4.21 patches
>>>>>> fio, 8KB random, 70% read, 30% write, 16 threads, iodepth=3D16
>>>>>>=20
>>>>>> Without this patch:
>>>>>>=20
>>>>>> read: IOPS=3D28.7k, BW=3D224MiB/s (235MB/s)(11.2GiB/51092msec)
>>>>>> write: IOPS=3D12.3k, BW=3D96.3MiB/s (101MB/s)(4918MiB/51092msec)
>>>>>>=20
>>>>>> With this patch:
>>>>>>=20
>>>>>> read: IOPS=3D28.6k, BW=3D224MiB/s (235MB/s)(11.2GiB/51276msec)
>>>>>> write: IOPS=3D12.3k, BW=3D95.8MiB/s (100MB/s)(4914MiB/51276msec)
>>>>>>=20
>>>>>> Seems like that's in the noise.
>>>>>=20
>>>>> Sigh. That's because it was the same kernel. Again, with
>>>>> feeling:
>>>>>=20
>>>>> 4.20.0-rc7-00048-g9274254:
>>>>> read: IOPS=3D28.6k, BW=3D224MiB/s (235MB/s)(11.2GiB/51276msec)
>>>>> write: IOPS=3D12.3k, BW=3D95.8MiB/s (100MB/s)(4914MiB/51276msec)
>>>>>=20
>>>>> 4.20.0-rc7-00049-ga4dea15:
>>>>> read: IOPS=3D27.2k, BW=3D212MiB/s (223MB/s)(11.2GiB/53979msec)
>>>>> write: IOPS=3D11.7k, BW=3D91.1MiB/s (95.5MB/s)(4917MiB/53979msec)
>>>>>=20
>>>>=20
>>>> So about a 5% reduction in performance?
>>>=20
>>> On this workload, yes.
>>>=20
>>> Could send the record marker in xs_send_kvec with the head[0]
>>> iovec.
>>> I'm going to try that next.
>>=20
>> That helps:
>>=20
>> Linux 4.20.0-rc7-00049-g664f679 #651 SMP Thu Jan 3 17:35:26 EST 2019
>>=20
>>   read: IOPS=3D28.7k, BW=3D224MiB/s (235MB/s)(11.2GiB/51185msec)
>>  write: IOPS=3D12.3k, BW=3D96.1MiB/s (101MB/s)(4919MiB/51185msec)
>>=20
>=20
> 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